Add sidebar link to thrift-python exception hierarchy page.

Summary: To make the [thrift-python exceptions type hierarchy](https://www.internalfb.com/intern/staticdocs/thrift/docs/fb/languages/python/api/exceptions/) page more discoverable, add the sidebar link to it.

Reviewed By: yoney

Differential Revision: D67680484

fbshipit-source-id: a0044a0e2af9441f6913947cf3c1d324537438d0

thrift/website/sidebars.js

@@ -284,6 +284,7 @@ module.exports = {
             items: [
               'fb/languages/python/code-frameworks',
               'fb/languages/python/python-capi',
+              'fb/languages/python/api/exceptions',
             ],
           },
         ]),