Add context when changing secret_key_base

Fixes rails#47060

Adds additional context of what it will be lost in case the `secret_key_base` changes.

Author: kinduff

guides/source/security.md

@@ -115,7 +115,14 @@ In test and development applications get a `secret_key_base` derived from the ap
 secret_key_base: 492f...
 ```
 
-WARNING: If your application's secrets may have been exposed, strongly consider changing them. Changing `secret_key_base` will expire currently active sessions.
+WARNING: If your application's secrets may have been exposed, strongly consider
+changing them. Note that changing `secret_key_base` will expire currently active
+sessions and require all users to log in again. In addition to session data, the
+following things may also be affected:
+
+* Encrypted cookies
+* Signed cookies
+* Active Storage Files
 
 ### Rotating Encrypted and Signed Cookies Configurations