添加markdown解析器，以后使用markdown写帮助文档

app/src/main/assets/web/help/index.html

@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<html>
+	<head>
+		<meta charset="utf-8" />
+		<title>help</title>
+		<link rel="stylesheet" href="css/github-markdown-light.min.css" />
+		<link rel="stylesheet" href="css/highlight.min.css" />
+		<style>
+			body {
+				min-width: 200px;
+				max-width: 980px;
+				margin: 0 auto;
+				padding: 45px;
+			}
+		</style>
+		<script src="js/require.js" data-main="js/main" defer async="true"></script>
+	</head>
+	<body>
+		<div id="mdviewer" class="markdown-body"></div>
+	</body>
+</html>