Two of the recommended plugins got merged in 1.4, and don’t exist any longer,
and when using flatpak the plugins must be installed that way.

* Create migrating_to_new_device.md

* Add link to Readme for further information.

* Added some info

* Make separate backup guide and integrate Readme information with new guides.

Co-authored-by: Licaon_Kter <licaon-kter@users.noreply.github.com>

fixes #4053

* various spelling fixes

* Fix typo

* Update README.md