Add backrest to backups category of README.md

[garethgeorge]

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Please take some time to answer the following questions as best you can:

• Why is it awesome?

Backrest is gaining significant popularity in the selfhosted community (particularly r/selfhosted) and builds on established reliable tools e.g. restic for storage. The significant contribution is that, prior to backrest, there was not a widely accepted webUI for configuring restic and automating backup operations. Backrest makes this process easy and makes restic significantly more approachable, especially for self-hosted users.

• Have you used it? For how long?

Backrest has been available for just over a year.

• Is this in a personal or professional setup?

Backrest is primarily self-hosted but I am aware of some professional installs and educational institutions using the software.

• How many devices/users/services/... do you manage with it?

To answer slightly orthoganally since I maintain the software , the install stats are

~250k downloads on docker hub and ~15k bare metal installs via direct download.

• Biggest pros/cons compared to other solutions?

Backrest is not designed to be a desktop native UI, there are some other projects that attempt this e.g. NpBackup or Restic-Browser. Backrest specifically targets web deployments (though it can also be installed on laptop devices and windows machines) where your browser is the primary interface client.