This section fixes the quick-start project such that uploaded avatar
images are not leaked and are cleaned up on user deletion, too.
For a newbie such as me, such information would have been super helpful to
get kicked off with consistent database/storage management.
- Changed instructions to use .env to .env.local (.env is not in .gitignore by default, whereas .env.local is. process still starts properly with .env.local.
- updated a couple of "edit this filename.js" to "edit this src/filename.js"
- added instructions to specify which files to update for Account.js and supabaseClient.js
- updated the "Add the new widget" src/Account.js sample code to better show where to add Avatar code and fit into existing code