Command descriptions and README update (add an admin)

README.md

     # If True, LDAP own tracim group managment (not available for now!)
     ldap_group_enabled = False
 
+You may need an administrator account to manage Tracim. Use the following command (from ``/install/dir/of/tracim/tracim``):
+
+```
+gearbox user create -l admin-email@domain.com -p new_password -g managers -g administrators
+```
+
+Keep in mind ``admin-email@domain.com`` must match with LDAP user.
+
 #### Other parameters  ####
 
 There are other parameters which may be of some interest for you. For example, you can:

tracim/tracim/command/ldap_test_server.py

 
 
 class LDAPTestServerCommand(Command):
+
+    def get_description(self):
+        return '''Run a test LDAP server.'''
+
     def take_action(self, parsed_args):
         # TODO - B.S. - 20160210: paramètre argv pour preciser les fixtures
         server = LdapServer(ldap_test_server_fixtures)

tracim/tracim/command/user.py

         self._user_api = UserApi(None)
         self._group_api = GroupApi(None)
 
+    def get_description(self):
+        return '''Create or update user.'''
+
     def get_parser(self, prog_name):
         parser = super().get_parser(prog_name)
 
         )
 
         parser.add_argument(
-            "-u",
-            "--update",
-            help='Update user password if exist',
-            dest='update',
-            action='store_true'
-        )
-
-        parser.add_argument(
             "-g",
             "--add-to-group",
             help='Add user to group',