contrib : add notes about merging PRs (#15881)

* contrib : add notes about merging PRs

* Update CONTRIBUTING.md

Co-authored-by: Diego Devesa <slarengh@gmail.com>

* Update CONTRIBUTING.md

Co-authored-by: Johannes Gäßler <johannesg@5d6.de>

---------

Co-authored-by: Diego Devesa <slarengh@gmail.com>
Co-authored-by: Johannes Gäßler <johannesg@5d6.de>

CONTRIBUTING.md

@@ -16,6 +16,9 @@
 - Use the following format for the squashed commit title: `<module> : <commit title> (#<issue_number>)`. For example: `utils : fix typo in utils.py (#1234)`
 - Optionally pick a `<module>` from here: https://github.com/ggml-org/llama.cpp/wiki/Modules
 - Consider adding yourself to [CODEOWNERS](CODEOWNERS)
+- Let authors, who are also collaborators, merge their own PRs
+- When merging a PR by a contributor, make sure you have a good understanding of the changes
+- Be mindful of maintenance: most of the work going into a feature happens after the PR is merged. If the PR author is not committed to contribute long-term, someone else needs to take responsibility (you)
 
 # Coding guidelines