Add a note about typings install (#437)

katowulf · davideast · commit 13a5e1e54871 · 2016-08-15T16:35:37.000-07:00
Devs may need to run `typings install` before npm run build.
diff --git a/CONTRIBUTOR.md b/CONTRIBUTOR.md
@@ -34,3 +34,8 @@ $ npm run docs
 $ cd docs
 $ firebase deploy
 ```
+
+## Error TS6053: File '...index.d.ts' not found.
+
+You may need to run `typings install`
+
