Add home page url to manifest.json

manifest.json

@@ -96,6 +96,7 @@
         "48" : "/images/icon48.png",
         "128": "/images/icon128.png"
     },
+    "homepage_url": "https://chrome.google.com/webstore/detail/markdown-viewer/ckkdlimhmcjmikdlpkmbgfkaikojcbjk",
 
     "permissions": [
         "tabs",