add comments regarding RCTPackagerConnection's reconnect (#53558)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/53558

Changelog: [Internal]
Got confused regarding why "reconnect" does not actually trigger a reconnect. It turns out, it only triggers a reconnect if the URL has changed.

Reviewed By: cipolleschi, huntie

Differential Revision: D80629308

fbshipit-source-id: 098ef5e91f3748deb9bc707b79bc0395d2442ca4