Add langgraph.json snippet to concept doc (#2630)

libs/checkpoint-postgres/langgraph/store/postgres/aio.py

@@ -99,6 +99,11 @@ class AsyncPostgresStore(AsyncBatchedBaseStore, BasePostgresStore[_ainternal.Con
         1. Call `setup()` before first use to create necessary tables and indexes
         2. Have the pgvector extension available to use vector search
         3. Use Python 3.10+ for async functionality
+
+    Note:
+        Semantic search is disabled by default. You can enable it by providing an `index` configuration
+        when creating the store. Without this configuration, all `index` arguments passed to
+        `put` or `aput`will have no effect.
     """
 
     __slots__ = (

libs/checkpoint-postgres/langgraph/store/postgres/base.py

@@ -573,7 +573,11 @@ class PostgresStore(BaseStore, BasePostgresStore[_pg_internal.Conn]):
 
         # Search by similarity
         results = store.search(("docs",), query="python programming")
-        ```
+
+    Note:
+        Semantic search is disabled by default. You can enable it by providing an `index` configuration
+        when creating the store. Without this configuration, all `index` arguments passed to
+        `put` or `aput`will have no effect.
 
     Warning:
         Make sure to call `setup()` before first use to create necessary tables and indexes.