Adds progress bar using tqdm to directory_loader (#3349)

Approach copied from `WebBaseLoader`. Assumes the user doesn't have
`tqdm` installed.

docs/modules/indexes/document_loaders/examples/directory_loader.ipynb

@@ -68,6 +68,51 @@
     "len(docs)"
    ]
   },
+  {
+   "attachments": {},
+   "cell_type": "markdown",
+   "id": "e633d62f",
+   "metadata": {},
+   "source": [
+    "## Show a progress bar"
+   ]
+  },
+  {
+   "attachments": {},
+   "cell_type": "markdown",
+   "id": "43911860",
+   "metadata": {},
+   "source": [
+    "By default a progress bar will not be shown. To show a progress bar, install the `tqdm` library (e.g. `pip install tqdm`), and set the `show_progress` parameter to `True`."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 10,
+   "id": "bb93daac",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Requirement already satisfied: tqdm in /Users/jon/.pyenv/versions/3.9.16/envs/microbiome-app/lib/python3.9/site-packages (4.65.0)\n"
+     ]
+    },
+    {
+     "name": "stderr",
+     "output_type": "stream",
+     "text": [
+      "0it [00:00, ?it/s]\n"
+     ]
+    }
+   ],
+   "source": [
+    "%pip install tqdm\n",
+    "loader = DirectoryLoader('../', glob=\"**/*.md\", show_progress=True)\n",
+    "docs = loader.load()"
+   ]
+  },
   {
    "cell_type": "markdown",
    "id": "c5652850",