Add issue template

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,21 @@
+---
+name: Bug report
+about: Please follow this template when submitting your issue
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+### Describe the issue
+
+[Be as clear as possible: nobody can read mind, and nobody is looking at your issue over your shoulder.]
+
+### Screenshot(s)
+
+[Screenshot(s) for difficult to describe visual issues.]
+
+### Versions
+
+- OS/version: [here]
+- GTK+ and/or application versions: [here]