Adding best practices to a few md files

Signed-off-by: Jonah Kowall <[email protected]>

MAINTAINERS.md

@@ -6,6 +6,22 @@
 
 This document contains a list of maintainers in this repo. See [opensearch-project/.github/RESPONSIBILITIES.md](https://github.com/opensearch-project/.github/blob/main/RESPONSIBILITIES.md#maintainer-responsibilities) that explains what the role of maintainer means, what maintainers do in this and other repos, and how they should be doing it. If you're interested in contributing, and becoming a maintainer, see [CONTRIBUTING](CONTRIBUTING.md).
 
+## Merging PRs
+OpenSearch pull requests are merged after there is approval from at least 1 maintainer. 
+
+Each PR should have:
+
+* A descriptive title, known as ["commit message"][good-commit-msg]. In summary:
+  * Limit the title to 50 characters
+  * Capitalize the title
+  * Do not end the title with a period
+  * Use the imperative mood in the title
+* A description of the problem it is solving. It could be simply a reference to the corresponding issue, e.g. `Resolves #123`.
+* A summary of changes made to solve the problem. Explain _what_ and _why_ instead of _how_.
+
+Merge the PR by using "Squash and merge" option on Github. Avoid creating merge commits.
+After the merge make sure referenced issues were closed.
+
 ## Current Maintainers
 
 | Maintainer         | GitHub ID                                                 | Affiliation |