Command Palette: fix sample links in README.md (#39983)

Fix links to sample folders.

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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
Two links were broken in the Command Palette readme because of a folder
name being "Exts" instead of "ext".

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## PR Checklist

- [ ] **Closes:** #xxx
- [ ] **Communication:** I've discussed this with core contributors
already. If 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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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments
N/A

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

Manually confirmed the following links are correct:


https://github.com/microsoft/PowerToys/tree/main/src/modules/cmdpal/ext/SamplePagesExtension

https://github.com/microsoft/PowerToys/tree/main/src/modules/cmdpal/ext/ProcessMonitorExtension

src/modules/cmdpal/README.md

@@ -39,8 +39,8 @@ Projects of interest are:
 
 
 [Initial SDK Spec]: ./doc/initial-sdk-spec/initial-sdk-spec.md
-[generic samples]: ./Exts/SamplePagesExtension 
-[real samples]: ./Exts/ProcessMonitorExtension
+[generic samples]: ./ext/SamplePagesExtension 
+[real samples]: ./ext/ProcessMonitorExtension
 [real extensions that we've "shipped" already]: https://github.com/zadjii/CmdPalExtensions/blob/main/src/extensions