Update backup.md

Add guide written by @ddyykk.

Author: JC5

docs/docs/how-to/firefly-iii/advanced/backup.md

@@ -5,6 +5,8 @@ Firefly III does not come with a built-in backup routine. Using your native OS t
 !!! warning "Do not use the export function as a backup mechanism"
     The export function of Firefly III is *not* a backup mechanism
 
+GitHub user [@ddyykk](https://github.com/ddyykk) has written excellent [this backup guide](https://github.com/orgs/firefly-iii/discussions/9960) with some scripts too. Check it out!
+
 ## Self-managed installation backup
 
 Grab the following and store it somewhere safe: