oss: update weaviate (#493)

Fixes langchain-ai/langchain#32774

Author: mdrxy

src/oss/python/integrations/vectorstores/weaviate.mdx

@@ -34,6 +34,20 @@ Some Weaviate instances, such as those running on WCS, have authentication enabl
 
 Read the [client authentication guide](https://weaviate.io/developers/weaviate/client-libraries/python#authentication) for more information, as well as the [in-depth authentication configuration page](https://weaviate.io/developers/weaviate/configuration/authentication).
 
+### Connect to an existing collection (reuse an index)
+
+If you already created a collection in your local Weaviate instance, you can connect to it directly:
+
+```python
+from langchain_weaviate import WeaviateVectorStore
+
+store = WeaviateVectorStore(
+    client=weaviate_client,
+    index_name="Test",
+    text_key="text",
+)
+```
+
 ## Installation
 
 ```python