Update docs -- Enabling suggestions to update pull request branches

[daniel-montalvo]

Ref: https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/managing-suggestions-to-update-pull-request-branches + related knowledgebase articles

I think this would be useful. We should discuss if we want to update head branches via traditional merge or by rebasing.

Anyone who don't want this enabled?

[daniel-montalvo]

Will do with rebasing.

[daniel-montalvo]

Done. For example, see #2395

Now we have:

• "update branch" button -- updates via merge
• "Update branch options" menu -- allows to select either merge or rebase.

[daniel-montalvo]

Daniel to write up the updates to the docs