[WIP] Add link to AngularDart API docs

Author: kwalrath

public/docs/dart/latest/index.jade

@@ -33,3 +33,6 @@ class="docs-landing")
         footer
           a(href="/docs/#{current.path[1]}/#{current.path[2]}/api/" class="button md-button") View API
 
+.alert.is-helpful.
+  Not using Angular 2 yet? Perhaps you need the
+  <a href="https://www.dartdocs.org/documentation/angular/latest" target="_blank">API docs for the original AngularDart</a>.