add disclaimer to gists about gist-ids

Author: cedi

docs/reference/gist.md

@@ -4,6 +4,19 @@ This is done using the `github/gist` backup type in your configuration file,
 along with an appropriate `from` directive to define the source of the gists
 you wish to back up.
 
+::: note
+GitHub Gists don't have explicit "names" — instead, they are identified by a unique *gist ID*.
+While GitHub displays a filename as the Gist name in the UI, it's actually just the name of the
+*first* file in the Gist, which can change over time.
+
+When backing up a Gist, the repository name will be based on the stable gist ID rather than a
+filename. This avoids issues where users rename files or add new ones, which could otherwise
+result in the same Gist being backed up multiple times under different names.
+
+If you choose to back up GitHub Gists, be aware that the resulting repositories will be named
+using their gist ID rather than the more human-readable names shown on the GitHub website.
+:::
+
 ## Examples
 The following examples show how you can combine the `kind` and `from` directives
 to back up gists from GitHub.