README: Document that cgo is not supported.

dmitshur · web-flow · commit f8a2b69c8c11 · 2016-09-10T22:39:53.000-07:00
Fixes #515.
diff --git a/README.md b/README.md
@@ -6,7 +6,7 @@ GopherJS - A compiler from Go to JavaScript
 GopherJS compiles Go code ([golang.org](https://golang.org/)) to pure JavaScript code. Its main purpose is to give you the opportunity to write front-end code in Go which will still run in all browsers. Give GopherJS a try on the [GopherJS Playground](http://gopherjs.github.io/playground/).
 
 ### What is supported?
-Nearly everything, including Goroutines ([compatibility table](https://github.com/gopherjs/gopherjs/blob/master/doc/packages.md)). Performance is quite good in most cases, see [HTML5 game engine benchmark](https://ajhager.github.io/engi/demos/botmark.html).
+Nearly everything, including Goroutines ([compatibility table](https://github.com/gopherjs/gopherjs/blob/master/doc/packages.md)). Performance is quite good in most cases, see [HTML5 game engine benchmark](https://ajhager.github.io/engi/demos/botmark.html). Cgo is not supported.
 
 ### Installation and Usage
 Get or update GopherJS and dependencies with:
