Npm docs setup (#834)

* added vuepress to package json
* use vuepress from package json

package.json

@@ -2,5 +2,8 @@
   "scripts": {
     "docs:dev": "vuepress dev docs",
     "docs:build": "vuepress build docs"
+  },
+  "devDependencies": {
+    "vuepress": "^1.7.1"
   }
 }