chore: update README.md and CONTRIBUTING.md (#4218)

- Moved the CONTRIBUTING.md file to project root.
- Fixed broken nightly release link.
- Update README.md

CONTRIBUTING.md

@@ -21,7 +21,7 @@ For questions on how to use PostgREST, please use
 ### Reporting an Issue
 
 * Make sure you test against the latest [stable release](https://github.com/PostgREST/postgrest/releases/latest)
-  and also against the latest [nightly release](https://github.com/PostgREST/postgrest/releases/tag/nightly).
+  and also against the latest [devel release](https://github.com/PostgREST/postgrest/releases/tag/devel).
   It is possible we already fixed the bug you're experiencing.
 
 * Provide steps to reproduce the issue, including your OS version and

README.md

@@ -142,6 +142,10 @@ You can help PostgREST ongoing maintenance and development by making a regular d
 
 Every donation will be spent on making PostgREST better for the whole community.
 
+## Contributing
+
+Contributions are always welcome and appreciated. Please see the [Contributing guidelines](https://github.com/PostgREST/postgrest/blob/main/CONTRIBUTING.md).
+
 ## Thanks
 
 The PostgREST organization is grateful to:

docs/index.rst

@@ -258,4 +258,4 @@ Testimonials
 Contributing
 ------------
 
-Please see the `Contributing guidelines <https://github.com/PostgREST/postgrest/blob/main/.github/CONTRIBUTING.md>`_ in the main PostgREST repository.
+Please see the `Contributing guidelines <https://github.com/PostgREST/postgrest/blob/main/CONTRIBUTING.md>`_ in the main PostgREST repository.