Update create_conference parameter to name

We can generate a slug from the name,
but we can't generate a name from the slug.

src/core/management/commands/create_conference.py

@@ -341,16 +341,16 @@ def _validate_date(s: str) -> datetime:
 class Command(BaseCommand):
     def add_arguments(self, parser):
         parser.add_argument(
-            'slug',
+            'name',
             type=str,
             nargs='?',
-            help='The url slug of the new conference.',
+            help='The name of the new conference',
         )
         parser.add_argument(
-            '-n',
-            '--name',
+            '-s',
+            '--slug',
             type=str,
-            help='The name of the new conference',
+            help='The url slug of the new conference. If not given, it will be slugified from the name.',
         )
         parser.add_argument(
             '-y',