borg upgrade: add to docs that only LOCAL repos are supported

borg/archiver.py

@@ -1210,6 +1210,8 @@ class Archiver:
         This currently supports converting an Attic repository to Borg and also
         helps with converting Borg 0.xx to 1.0.
 
+        Currently, only LOCAL repositories can be upgraded (issue #465).
+
         It will change the magic strings in the repository's segments
         to match the new Borg magic strings. The keyfiles found in
         $ATTIC_KEYS_DIR or ~/.attic/keys/ will also be converted and

docs/usage/upgrade.rst.inc

@@ -38,6 +38,8 @@ Upgrade an existing Borg repository.
 This currently supports converting an Attic repository to Borg and also
 helps with converting Borg 0.xx to 1.0.
 
+Currently, only LOCAL repositories can be upgraded (issue #465).
+
 It will change the magic strings in the repository's segments
 to match the new Borg magic strings. The keyfiles found in
 $ATTIC_KEYS_DIR or ~/.attic/keys/ will also be converted and