[Doc] add introduction page (#452)

package.json

@@ -72,7 +72,7 @@
     "dependency-tree": "^5.12.0",
     "eslint-plugin-vue": "^2.1.0",
     "extract-text-webpack-plugin": "3.0.2",
-    "fast-vue-md-loader": "^1.0.2",
+    "fast-vue-md-loader": "^1.0.3",
     "felint": "^0.5.0-alpha.3",
     "file-save": "^0.2.0",
     "friendly-errors-webpack-plugin": "^1.6.1",
@@ -105,7 +105,7 @@
     "run-sequence": "^2.1.0",
     "sinon": "^2.4.1",
     "sinon-chai": "^2.12.0",
-    "style-loader": "^0.19.0",
+    "style-loader": "^0.19.1",
     "uppercamelcase": "^3.0.0",
     "url-loader": "^0.6.2",
     "vant-doc": "0.3.19",