[Doc] Add doc for a script to build installer locally, and doc for testing winget install locally (#40805)

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fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request

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## PR Checklist

- [ ] Closes: #xxx
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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## Detailed Description of the Pull Request / Additional comments
1. Add instructions to build installer locally with a script
2. Add doc explaining how to install an installer by winget locally.
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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

doc/devdocs/core/installer.md

@@ -87,6 +87,13 @@
 
 ### Building PowerToys Locally
 
+#### One stop script for building installer
+1. Open developer powershell for vs 2022
+2. Run tools\build\build-installer.ps1
+> For the first-time setup, please run the installer as an administrator. This ensures that the Wix tool can move wix.target to the desired location and trust the certificate used to sign the MSIX packages.
+
+The following manual steps will not install the MSIX apps (such as Command Palette) on your local installer.
+
 #### Prerequisites for building the MSI installer
 
 1. Install the [WiX Toolset Visual Studio 2022 Extension](https://marketplace.visualstudio.com/items?itemName=WixToolset.WixToolsetVisualStudio2022Extension).