Add issue template for bug reports.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,18 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: "[BUG]"
+labels: bug
+assignees: fpetrogalli
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is. Please add references to the documents where the bug is.
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem. This is useful for layout problems in the PDF or HTML pages.
+
+**Our commitment**
+
+We will work to solve the bug report in time for the upcoming release. However, we would like to encourage you to submit the fix yourself, if possible. If you intend to do so and this is your first contribution, we recommend reading our [contribution guidelines](https://github.com/ARM-software/acle).