Update issue templates for bug reports

Author: Robin Freyler

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,21 @@
+---
+name: Bug report
+about: Create a report to help Wasmi improve
+title: ''
+labels: bug
+assignees: ''
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**To Reproduce**
+Steps to reproduce the behavior:
+
+1. What Wasmi version was used?
+2. Bug occurs on Wasmi CLI or Wasmi library?
+3. Ideally please provide minified Wasm (`.wasm`) or Wat (`.wat`) file to reproduce.