Update migration_group_import_only.py

migration_group_import_only.py

 #!/usr/bin/env python3
+"""\
+Import a group from source(pilot) GitLab to new GitLab
+
+Usage: migration_group_import_only.py
+
+Author: Donghee Kang
+Email : donghee.kang@kit.edu
+"""
+
 import gitlab
 import os
 import sys
@@ -113,4 +122,4 @@ if __name__ == "__main__":
 
     # let's start collecting project information
     migration_accessor = migration()
-    migration_accessor.import_projects()
\ No newline at end of file
+    migration_accessor.import_projects()