Clarify the necessity to separately backup key in repokey mode (#4237)

clarify the necessity to separately backup key in repokey mode

src/borg/archiver.py

@@ -258,11 +258,19 @@ class Archiver:
                 'for details about the security implications.', shlex.quote(path))
 
         if key.NAME != 'plaintext':
-            logger.warning(
-                '\n'
-                'IMPORTANT: you will need both KEY AND PASSPHRASE to access this repo!\n'
-                'Use "borg key export" to export the key, optionally in printable format.\n'
-                'Write down the passphrase. Store both at safe place(s).\n')
+            if 'repokey' in key.NAME:
+                logger.warning(
+                    '\n'
+                    'IMPORTANT: you will need both KEY AND PASSPHRASE to access this repo!\n'
+                    'The key is included in the repository config, but should be backed up in case the repository gets corrupted.\n'
+                    'Use "borg key export" to export the key, optionally in printable format.\n'
+                    'Write down the passphrase. Store both at safe place(s).\n')
+            else:
+                logger.warning(
+                    '\n'
+                    'IMPORTANT: you will need both KEY AND PASSPHRASE to access this repo!\n'
+                    'Use "borg key export" to export the key, optionally in printable format.\n'
+                    'Write down the passphrase. Store both at safe place(s).\n')
         return self.exit_code
 
     @with_repository(exclusive=True, manifest=False)