Update manual.rst

`key remove` becomes `key rm`.

doc/manual.rst

@@ -678,7 +678,7 @@ Manage repository keys
 ----------------------
 
 The ``key`` command allows you to set multiple access keys or passwords
-per repository. In fact, you can use the ``list``, ``add``, ``remove``
+per repository. In fact, you can use the ``list``, ``add``, ``rm``
 and ``passwd`` sub-commands to manage these keys very precisely:
 
 .. code-block:: console