impromptu: add versionadded info in doc

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

doc/source/commands.rst

@@ -223,6 +223,8 @@ These commands work in *any* tab.
 
         Invite specified JIDs into a newly created room.
 
+       .. versionadded:: 0.13
+
     /activity
         **Usage:** ``/activity [<general> [specific] [comment]]``
 
@@ -483,6 +485,8 @@ Normal Conversation tab commands
         Invite specified JIDs, with this contact, into a newly
         created room.
 
+       .. versionadded:: 0.13
+
 .. _rostertab-commands:
 
 Contact list tab commands