Update docs to remind to npm install before npm run build.

Change-Id: I13a7f456ee99ea7e84e7caaa1ce6efc6da6ce799
diff --git a/README.md b/README.md
index fc965b7..a01cad1 100644
--- a/README.md
+++ b/README.md
@@ -18,6 +18,7 @@
 ### BUILD
 
 ```
+npm install
 npm run build
 ```