chore: add issue template

yyx990803 · yyx990803 · commit cd214cef7257 · 2018-01-13T13:19:09.000-05:00
diff --git a/.github/ISSUE_TEMPLATE.md b/.github/ISSUE_TEMPLATE.md
@@ -0,0 +1,7 @@
+<!--
+IMPORTANT: Please use the following link to create a new issue:
+
+  https://new-issue.vuejs.org/?repo=vuejs/vue-test-utils
+
+If your issue was not created using the app above, it will be closed immediately.
+-->
