Added GitHub button

Author: a7ul

book.json

@@ -8,7 +8,8 @@
     "ga",
     "edit-link",
     "back-to-top-button",
-    "githubcontributors"
+    "githubcontributors",
+    "github-buttons"
   ],
   "pdf": {
     "paperSize": "a4"
@@ -27,6 +28,14 @@
     },
     "ga": {
       "token": "UA-111146084-1"
-    }
+    },
+    "github-buttons": {
+     "buttons": [{
+       "user": "react-made-native-easy",
+       "repo": "book",
+       "type": "star",
+       "size": "small"
+     }]
+   }
   }
 }