chore: more instructions on repository syncing

[hoxyq]

Summary

Added more instructions to the README.md file about how to perform repository syncing.

Test plan

• This change maintains backwards compatibility with previous Local Storage data (if modifying settings, experiments, or other persisted client state).

Upstreaming plan

• This commit should be sent as a patch to the upstream devtools-frontend repo. I've reviewed the contribution guide.
• This commit is React Native-specific and cannot be upstreamed.

[huntie]

❤️