package.json: add description and homepage fields

package.json

 {
   "name": "next",
   "version": "0.9.9",
-  "description": "",
+  "description": "Next.js is a minimalistic framework for server-rendered React applications",
   "main": "./dist/lib/index.js",
+  "homepage": "https://github.com/zeit/next.js",
   "license": "MIT",
   "files": [
     "dist"