Added documentation for add_texts function for Pinecone integration (#7134)

- Description: added some documentation to the Pinecone vector store
docs page.
- Issue: #7126 
- Dependencies: None
- Tag maintainer: @baskaryan 

I can add more documentation on the Pinecone integration functions as I
am going to go in great depth into this area. Just wanted to check with
the maintainers is if this is all good.

docs/extras/modules/data_connection/vectorstores/integrations/pinecone.ipynb

@@ -1,6 +1,7 @@
 {
  "cells": [
   {
+   "attachments": {},
    "cell_type": "markdown",
    "id": "683953b3",
    "metadata": {},
@@ -51,6 +52,7 @@
    ]
   },
   {
+   "attachments": {},
    "cell_type": "markdown",
    "id": "320af802-9271-46ee-948f-d2453933d44b",
    "metadata": {},
@@ -136,6 +138,30 @@
     "print(docs[0].page_content)"
    ]
   },
+  {
+   "attachments": {},
+   "cell_type": "markdown",
+   "id": "86a4b96b",
+   "metadata": {},
+   "source": [
+    "### Adding More Text to an Existing Index\n",
+    "\n",
+    "More text can embedded and upserted to an existing Pinecone index using the `add_texts` function\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "38a7a60e",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "index = pinecone.Index(\"langchain-demo\")\n",
+    "vectorstore = Pinecone(index, embeddings.embed_query, \"text\")\n",
+    "\n",
+    "vectorstore.add_texts(\"More text!\")"
+   ]
+  },
   {
    "attachments": {},
    "cell_type": "markdown",