[doc] Update README

* Add example command for running Docker container as a non-root userx
* Update syntax highlighing

README.md

@@ -18,19 +18,27 @@ them in a terminal as well as in a web browser.
 
 Install latest version ([other installation options](#installation)):
 
-    sudo pip3 install asciinema
+```sh
+pip3 install asciinema
+```
 
 Record your first session:
 
-    asciinema rec first.cast
+```sh
+asciinema rec first.cast
+```
 
 Now replay it with double speed:
 
-    asciinema play -s 2 first.cast
+```sh
+asciinema play -s 2 first.cast
+```
 
 Or with normal speed but with idle time limited to 2 seconds:
 
-    asciinema play -i 2 first.cast
+```sh
+asciinema play -i 2 first.cast
+```
 
 You can pass `-i 2` to `asciinema rec` as well, to set it permanently on a
 recording. Idle time limiting makes the recordings much more interesting to
@@ -38,7 +46,9 @@ watch. Try it.
 
 If you want to watch and share it on the web, upload it:
 
-    asciinema upload first.cast
+```sh
+asciinema upload first.cast
+```
 
 The above uploads it to [asciinema.org](https://asciinema.org), which is a
 default [asciinema-server](https://github.com/asciinema/asciinema-server)
@@ -47,7 +57,9 @@ browser.
 
 You can record and upload in one step by omitting the filename:
 
-    asciinema rec
+```sh
+asciinema rec
+```
 
 You'll be asked to confirm the upload when the recording is done. Nothing is
 sent anywhere without your consent.
@@ -55,6 +67,7 @@ sent anywhere without your consent.
 These are the basics, but there's much more you can do. The following sections
 cover installation, usage and hosting of the recordings in more detail.
 
+
 ## Installation
 
 ### Python package
@@ -62,7 +75,9 @@ cover installation, usage and hosting of the recordings in more detail.
 asciinema is available on [PyPI](https://pypi.python.org/pypi/asciinema) and can
 be installed with pip (Python 3 with setuptools required):
 
-    sudo pip3 install asciinema
+```sh
+pip3 install asciinema
+```
 
 This is the recommended way of installation, which gives you the latest released
 version.
@@ -80,32 +95,45 @@ can clone the repo and run asciinema straight from the checkout.
 
 Clone the repo:
 
-    git clone https://github.com/asciinema/asciinema.git
-    cd asciinema
+```sh
+git clone https://github.com/asciinema/asciinema.git
+cd asciinema
+```
 
 If you want latest stable version:
 
-    git checkout master
+```sh
+git checkout master
+```
 
 If you want current development version:
 
-    git checkout develop
+```sh
+git checkout develop
+```
 
 Then run it with:
 
-    python3 -m asciinema --version
+```sh
+python3 -m asciinema --version
+```
 
 ### Docker image
 
-asciinema Docker image is based on Ubuntu 18.04 and has the latest version of
+asciinema Docker image is based on [Ubuntu
+20.04](https://releases.ubuntu.com/20.04/) and has the latest version of
 asciinema recorder pre-installed.
 
-    docker pull asciinema/asciinema
+```sh
+docker pull docker.io/asciinema/asciinema
+```
 
 When running it don't forget to allocate a pseudo-TTY (`-t`), keep STDIN open
 (`-i`) and mount config directory volume (`-v`):
 
-    docker run --rm -ti -v "$HOME/.config/asciinema":/root/.config/asciinema asciinema/asciinema rec
+```sh
+docker run --rm -it -v "${HOME}/.config/asciinema:/root/.config/asciinema" docker.io/asciinema/asciinema rec
+```
 
 Container's entrypoint is set to `/usr/local/bin/asciinema` so you can run the
 container with any arguments you would normally pass to `asciinema` binary (see
@@ -117,9 +145,26 @@ image from this one (start your custom Dockerfile with `FROM
 asciinema/asciinema`). Another option is to start the container with `/bin/bash`
 as the entrypoint, install extra packages and manually start `asciinema rec`:
 
-    docker run --rm -ti -v "$HOME/.config/asciinema":/root/.config/asciinema --entrypoint=/bin/bash asciinema/asciinema
-    root@6689517d99a1:~# apt-get install foobar
-    root@6689517d99a1:~# asciinema rec
+```console
+docker run --rm -it -v "${HOME}/.config/asciinema:/root/.config/asciinema" --entrypoint=/bin/bash docker.io/asciinema/asciinema rec
+root@6689517d99a1:~# apt-get install foobar
+root@6689517d99a1:~# asciinema rec
+```
+
+It is also possible to run the docker container as a non-root user, which has
+security benefits. You can specify a user and group id at runtime to give the
+application permission similar to the calling user on your host.
+
+```sh
+docker run --rm -it \
+    --env=ASCIINEMA_CONFIG_HOME="/run/user/$(id -u)/.config/asciinema" \
+    --user="$(id -u):$(id -g)" \
+    --volume="${HOME}/.config/asciinema:/run/user/$(id -u)/.config/asciinema:rw" \
+    --volume="${PWD}:/data:rw" \
+    --workdir='/data' \
+    docker.io/asciinema/asciinema rec
+```
+
 
 ## Usage
 
@@ -196,27 +241,37 @@ Following keyboard shortcuts are available:
 
 Playing from a local file:
 
-    asciinema play /path/to/asciicast.cast
+```sh
+asciinema play /path/to/asciicast.cast
+```
 
 Playing from HTTP(S) URL:
 
-    asciinema play https://asciinema.org/a/22124.cast
-    asciinema play http://example.com/demo.cast
+```sh
+asciinema play https://asciinema.org/a/22124.cast
+asciinema play http://example.com/demo.cast
+```
 
 Playing from asciicast page URL (requires `<link rel="alternate"
 type="application/x-asciicast" href="/my/ascii.cast">` in page's HTML):
 
-    asciinema play https://asciinema.org/a/22124
-    asciinema play http://example.com/blog/post.html
+```sh
+asciinema play https://asciinema.org/a/22124
+asciinema play http://example.com/blog/post.html
+```
 
 Playing from stdin:
 
-    cat /path/to/asciicast.cast | asciinema play -
-    ssh user@host cat asciicast.cast | asciinema play -
+```sh
+cat /path/to/asciicast.cast | asciinema play -
+ssh user@host cat asciicast.cast | asciinema play -
+```
 
 Playing from IPFS:
 
-    asciinema play dweb:/ipfs/QmNe7FsYaHc9SaDEAEXbaagAzNw9cH7YbzN4xV7jV1MCzK/ascii.cast
+```sh
+asciinema play dweb:/ipfs/QmNe7FsYaHc9SaDEAEXbaagAzNw9cH7YbzN4xV7jV1MCzK/ascii.cast
+```
 
 Available options:
 
@@ -391,6 +446,7 @@ source [contributors](https://github.com/asciinema/asciinema/contributors).
 
 ## License
 
-Copyright &copy; 2011–2019 Marcin Kulik.
+Copyright &copy; 2011–2021 Marcin Kulik.
 
-All code is licensed under the GPL, v3 or later. See LICENSE file for details.
+All code is licensed under the GPL, v3 or later. See [LICENSE](./LICENSE) file
+for details.