add known issue

README.md

@@ -2,6 +2,10 @@
 
 HackerNews clone built with Vue 2.0 + vue-router + vuex, with server-side rendering.
 
+## Known Issue
+
+`babel-preset-es2015-webpack` currently has a bug which will prevent the build from working. You can manually apply [this change](https://github.com/gajus/babel-preset-es2015-webpack/pull/13/files) to fix it before it gets a new release out.
+
 ## Build Setup
 
 ``` bash