Add langchain dev requirement

Author: cevian

settings.ini

@@ -27,10 +27,10 @@ language = English
 status = 3
 user = timescale
 requirements = asyncpg psycopg2 pgvector
-dev_requirements = python-dotenv
+dev_requirements = python-dotenv langchain
 readme_nb = index.ipynb
-allowed_metadata_keys = 
-allowed_cell_metadata_keys = 
+allowed_metadata_keys =
+allowed_cell_metadata_keys =
 jupyter_hooks = True
 clean_ids = True
 clear_all = False