chore(Readme): Add instructions how to test your PR with server

Signed-off-by: Joas Schilling <[email protected]>

README.md

@@ -15,3 +15,40 @@ Some 3rd party libraries that are necessary to run Nextcloud.
 7. Run `dump-autoload`
 8. Commit all changes onto a new branch
 9. You might need the following command for pushing if used as submodule: `git push [email protected]:nextcloud/3rdparty.git branchname`
+
+## Testing your PR with server
+
+1. On https://github.com/nextcloud/server make a new branch `3rdparty/my-dependency`
+2. Navigate into the 3rdparty directory
+3. Checkout the commit sha of the **last commit** of your PR in the 3rdparty repository
+4. Leave the directory
+5. Add the change to the stash
+6. Commit (with sign-off and message)
+7. Push the branch and send a PR
+8. ⏳ Wait for CI and reviews
+9. Navigate into the 3rdparty directory
+10. Checkout the commit sha of the **merge commit** of your PR in the 3rdparty repository
+11. Leave the directory
+12. Add the change to the stash
+13. Amend to the previous dependency bump
+14. Push with lease force
+15. ⏳ Wait for CI
+16. Merge 🎉
+
+```sh
+cd 3rdparty
+git checkout 16cd747ebb8ab4d746193416aa2448c8114d5084
+cd ..
+git add 3rdparty
+git commit
+git push origin 3rdparty/my-dependency
+
+# Wait for CI and reviews
+
+cd 3rdparty
+git checkout 54b63cc87af3ddb0ddfa331f20ecba5fcc01d495
+cd ..
+git add 3rdparty
+git commit --amend
+git push --force-with-lease origin 3rdparty/my-dependency
+```