authorized_key: Be more specific about manage_dir

- Explain which properties are managed when manage_dir is True.

library/system/authorized_key

@@ -48,7 +48,11 @@ options:
     version_added: "1.2"
   manage_dir:
     description:
-      - Whether this module should manage the directory of the authorized_keys file. Make sure to set C(manage_dir=no) if you are using an alternate directory for authorized_keys set with C(path), since you could lock yourself out of SSH access. See the example below.
+      - Whether this module should manage (create it, change owner and
+        permissions) the directory of the authorized_keys file. Make sure to
+        set C(manage_dir=no) if you are using an alternate directory for
+        authorized_keys set with C(path), since you could lock yourself out of
+        SSH access. See the example below.
     required: false
     choices: [ "yes", "no" ]
     default: "yes"