Add SwitchTransition to docs navigation

Author: silvenon

www/gatsby-config.js

@@ -16,6 +16,10 @@ module.exports = {
         displayName: 'CSSTransition',
         codeSandboxId: 'm77l2vp00x',
       },
+      {
+        path: '/switch-transition',
+        displayName: 'SwitchTransition',
+      },
       {
         path: '/transition-group',
         displayName: 'TransitionGroup',