Add code sample in Issue template

.github/ISSUE_TEMPLATE/bug_report.md

@@ -23,6 +23,9 @@ A clear and concise description of what you expected to happen.
 **Screenshots**
 If applicable, add screenshots to help explain your problem.
 
+**Code Sample**
+If applicable, add the code sample or a link to the [live editor](https://mermaid-js.github.io/mermaid-live-editor).
+
 **Desktop (please complete the following information):**
  - OS: [e.g. iOS]
  - Browser [e.g. chrome, safari]