flask: add link to book reference

Author: Marco Bakera

flask/flask.ipynb

@@ -1150,7 +1150,8 @@
     "\n",
     "* [Flask Quickstart](https://flask.palletsprojects.com/en/2.0.x/quickstart/)\n",
     "* [awesome flask](https://github.com/humiaozuzu/awesome-flask)\n",
-    "* [flask-autodoc](https://github.com/acoomans/flask-autodoc)"
+    "* [flask-autodoc](https://github.com/acoomans/flask-autodoc)\n",
+    "* [Building Web Apps with Python and Flask (Buch)](https://bpbonline.com/products/building-web-apps-with-python-and-flask?_pos=1&_sid=ad8ddb69d&_ss=r)"
    ]
   }
  ],
@@ -1170,7 +1171,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.9.5"
+   "version": "3.9.6"
   }
  },
  "nbformat": 4,

flask/flask_final.html

@@ -15486,6 +15486,7 @@ <h2 id="Weitere-Infos">Weitere Infos<a class="anchor-link" href="#Weitere-Infos"
 <li><a href="https://flask.palletsprojects.com/en/2.0.x/quickstart/">Flask Quickstart</a></li>
 <li><a href="https://github.com/humiaozuzu/awesome-flask">awesome flask</a></li>
 <li><a href="https://github.com/acoomans/flask-autodoc">flask-autodoc</a></li>
+<li><a href="https://bpbonline.com/products/building-web-apps-with-python-and-flask?_pos=1&amp;_sid=ad8ddb69d&amp;_ss=r">Building Web Apps with Python and Flask (Buch)</a></li>
 </ul>
 
 </div>