added plotly example source

Notebook/the-promise-to-partner-Workshop_python.ipynb

@@ -428,7 +428,7 @@
    "source": [
     "## Second Plot - Plotly\n",
     "\n",
-    "This is a little more complicated, but it does give a cleaner and interactive graph. It uses the edges and nodes defind in the networkx object `G` above."
+    "This is a little more complicated, but it does give a cleaner and interactive graph. It uses the edges and nodes defind in the networkx object `G` above. The below code relies heavily on [this example](<https://plotly.com/python/network-graphs/>)."
    ],
    "cell_type": "markdown",
    "metadata": {}