Added gitpod config

Author: svenefftinge

.gitpod.yml

@@ -0,0 +1,9 @@
+ports:
+- port: 3000
+  onOpen: ignore
+tasks:
+- command: >
+    while ! timeout 1 bash -c "echo > /dev/tcp/localhost/3000" 2>/dev/null ; do sleep 1; done &&
+    gp preview $(gp url 3000)babel/babel/blob/master/packages/babel-core/test/browserify.js
+- init: yarn
+  command: yarn start

readme.md

@@ -9,3 +9,7 @@ Browse the history of any file from GitHub with style
 </div>
 
 > Follow [@pomber](https://twitter.com/pomber) for updates
+
+Start coding and contributing using Gitpod, a free online dev environment.
+
+[![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/pomber/github-history)