Document changelog update script.

Author: janiversen

docs/CONTRIBUTING.md

@@ -196,6 +196,19 @@ work as expected.
 If the functionality you're working on does NOT depend on code from VS Code, please
 move it out and into code-server.
 
+### Prepare CHANGELOG.md for releases.
+
+prepare_changelog.py does:
+- extract merged PR´s from last release
+- Prepare CHANGELOG.md (needs manual editing to group the PRs)
+
+the script depend on `gh` which must be installed.
+
+example
+```
+./prepare_changelog.py 3.10.3 1.56.1 3393
+```
+
 ### Currently Known Issues
 
 - Creating custom VS Code extensions and debugging them doesn't work

docs/MAINTAINING.md

@@ -83,11 +83,7 @@ The code-server project follows traditional [semantic versioning](ttps://semver.
 
 ### Changelog
 
-To save time when creating a new release for code-server, we keep a running changelog at `CHANGELOG.md`.
-
-If either author or reviewer of a PR believe the change should be mentioned in the `CHANGELOG`, then it should be added.
-
-If there is not a "Next Version" when you modify `CHANGELOG`, please add it using the template you see near the top of `CHANGELOG`. You can use the suggested format: `<pr title> <pr #> <author> Example: `fix: Check the logged user instead of $USER #3330 @videlanicolas`
+To save time when creating a new release for code-server, we have a script that generates `CHANGELOG.md`.
 
 ## Release