[Quality/Performance] update capture cam README to reflect latest updates

[sync-by-unito]

Suggestion

Currently repo Capture Cam Getting Started is outdated.

1. NUMBERS_BUBBLE_DB_URL should be removed from README
2. add other env vars that are used but now reflected on README
3. update on how to start local copy of capture cam for new developers

┆Issue is synchronized with this Asana task by Unito
┆Created By: Sam