[yarn] Add yarn patch command to package.json

Summary:
Often you need to pull in tagged commits from origin (via git pull --all --tags) before arc patch to ensure that parent commits exist locally.

This isn't really "documented" anywhere and has come up from time to time on Phabricator/Linear/etc.

This yarn patch command should make things a bit more convenient in the future.

Test Plan:
Was able to yarn patch D5427 and get @ashoat's full ReactNav stack locally:

Reviewers: derek, ashoat, varun, O2 Blocking Reviewers

Reviewed By: derek, ashoat, O2 Blocking Reviewers

Subscribers: tomek, abosh, ashoat

Differential Revision: https://phab.comm.dev/D5445