make template compilation results selectable

Author: chrisvfritz

src/v2/guide/render-function.md

@@ -605,6 +605,10 @@ console.error = function (error) {
 }
 </script>
 <style>
+#vue-compile-demo {
+  -webkit-user-select: inherit;
+  user-select: inherit;
+}
 #vue-compile-demo pre {
   padding: 10px;
   overflow-x: auto;