Add “Keep your PR branch in sync with main” section (rebase/merge workflow)

[ronhedwigzape]

Right now the README covers cloning/branching/PRs, but it doesn’t explain how to update an in-progress feature branch when main has new commits. This often causes last-minute conflicts and uncertainty for contributors.

Proposal
Add a short section under General Workflow (after “Pull Requests” or “Code Review”) explaining two supported ways to sync a PR branch with the base branch:

1. Preferred (solo PR branches): Rebase onto latest origin/main

git fetch origin
git switch feat/<name>
git rebase origin/main
# resolve conflicts (if any)
git add <files>
git rebase --continue
git push --force-with-lease

Notes:

• Mention that rebasing rewrites commit SHAs, so force push is required; recommend --force-with-lease as the safer option.

2. Alternative (shared branches / no force-push teams): Merge origin/main into feature

git fetch origin
git switch feat/<name>
git merge origin/main
git push

Also include

• A quick note that GitHub PRs can be updated via the Update branch dropdown (merge or rebase) as an alternative to CLI.
• If the repo uses submodules: after syncing, run:

git submodule update --init --recursive

Acceptance criteria

• README contains the new “Keep your PR branch in sync with main” section
• Includes both rebase + merge command paths + when to choose each
• Mentions GitHub “Update branch” option
• Mentions submodule update command for repos like pillar/pillar-ui