* modify fly.io url to point to correct documentation

* Create 3113.md

* Add callouts to starting fresh and migration documentations

* README

* Update README

The "community documentation" link below Code Structure headline in
`README` will direct user to page not found error

Depends on https://github.com/actualbudget/docs/pull/202.

Replaced contributing link

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*   add demo image to the README

* Different image

Readme updates