add issue template (close #58)

Author: yyx990803

issue_template.md

@@ -0,0 +1,12 @@
+<!--
+
+IMPORTANT: Did the `vue init` command *itself* result in an error?
+
+  -> NO: If the files for a project template were correctly created, but did
+         not work out-of-the-box as you expected, please open an issue for the
+         appropriate template at github.com/vuejs-templates
+
+  -> YES: Open an issue here. Please include the exact command you used,
+          what you expected to happen, and what happened instead.
+
+-->