Add note about virtual columns for the future

lib/rollbot/injection/data.py

@@ -38,6 +38,7 @@ class DataStore(Generic[DataType]):
         ).strip("_")
 
     async def _setup(self):
+        # TODO virtual columns with indexes for certain types?
         await self.connection.execute(
             f'CREATE TABLE IF NOT EXISTS {self.table_name} ( \
                 key TEXT NOT NULL PRIMARY KEY, \