add: external readme

Author: ui2code

external/README.md

@@ -0,0 +1,18 @@
+# External Snippets
+
+## Analytics
+
+### [ga] Google Analytics Object
+
+```html
+<script>
+  (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
+  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
+  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
+  })(window,document,'script','//www.google-analytics.com/analytics.js','ga');
+
+  ga('create', '${1:UA-XXXXX-X}', 'auto');
+  ga('send', 'pageview');
+
+</script>$2
+```