Document the new deeplink format [2/n]

Summary:
Added docs on how to use deeplink.

Note that not all features are implemented yet.

Reviewed By: fabiomassimo

Differential Revision: D29845044

fbshipit-source-id: 835fba8ce97c2106d160f347675e11d1ed749fba

website/sidebars.js

@@ -105,6 +105,7 @@ module.exports = {
     'Desktop plugin APIs': [
       'extending/flipper-plugin',
       'extending/styling-components',
+      'extending/deeplinks',
       ...fbInternalOnly([
         {
           'QPL linting': ['fb/building-a-linter', 'fb/active-linters'],