Add docstring for time_db_transaction

webservice/webservice.py

@@ -304,6 +304,11 @@ def parse_config(cmd: List[str], config: Dict[str, Any]) -> List[str]:
 
 
 class time_db_transaction:
+    """Record time taken to write to the database
+
+    Use as a context manager. When leaving the block, the transaction will be
+    committed (or rolled back, on error), and the time taken logged.
+    """
     t_start = 0
 
     def __init__(self, conn: sqlite3.Connection, label: str):