Update index.html description

Author: charlescyt

web/index.html

@@ -18,7 +18,7 @@
 
     <meta charset="UTF-8" />
     <meta content="IE=Edge" http-equiv="X-UA-Compatible" />
-    <meta name="description" content="A new Flutter project." />
+    <meta name="description" content="A simple Dart AST node viewer built with Flutter." />
 
     <!-- iOS meta tags & icons -->
     <meta name="mobile-web-app-capable" content="yes" />