add documentation for migration command system

gs/POSTGRESQL_SETUP.md

@@ -67,6 +67,10 @@ Note: You can choose to remove the first to lines of the `.env` that start with
 
 Now, you can start the backend as by running `fastapi dev gs/backend/main.py` from the top level directory to run in development mode.
 
+To migrate pre-determined datainto your local database, you can run `python3 gs/backend/migrate.py` from the top level directory.
+
+Alternatively, you can include `callsigns` or `commands` as command arguments to migrate those respective datasets individually.
+
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 ## Sources

gs/backend/migrate.py

@@ -3,6 +3,16 @@
 from gs.backend.data.database.engine import get_db_session
 from gs.backend.data.resources.utils import add_callsigns, add_main_commands
 
+"""
+To migrate pre-determined datainto your local database,
+you can run `python3 gs/backend/migrate.py` from the top
+level directory.
+
+Alternatively, you can include `callsigns` or `commands`
+as command arguments to migrate those respective datasets
+individually.
+"""
+
 if __name__ == "__main__":
     if len(sys.argv) > 2:
         raise ValueError(f"Invalid input. Expected at most 1 argument, received {len(sys.argv)}")