Add syntax highlighting issue template

Author: nicolasstucki

.github/ISSUE_TEMPLATE/syntax-highlight.md

@@ -0,0 +1,13 @@
+---
+name: "Syntax highlighting"
+about: Please create a syntax highlighting issue here https://github.com/scala/vscode-scala-syntax/issues
+title: ''
+labels:
+assignees: ''
+
+---
+
+Please create a syntax highlighting issue here: [scala/vscode-scala-syntax](https://github.com/scala/vscode-scala-syntax/issues).
+
+
+