Add issue template

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,18 @@
+
+<!--
+
+THERE IS A 99% CHANCE YOU ARE FILING THIS ISSUE IN THE WRONG REPOSITORY.
+
+This is just the repository for the thin VS Code extension.
+
+If this issue is *not* directly related to the *integration* into VS Code,
+but a bug, feature request, performance issue, crash, etc. it needs to be filed
+in the repository of the *language server*:
+
+https://github.com/felixfbecker/php-language-server
+
+Most likely there is already an open issue, please search for one first.
+
+Thank you.
+
+-->