Create issue template (#74)

* Create issue template

* Ask for OS

* Update bug_report.md

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,26 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**Software**
+OS and version (e.g. Ubuntu 20.04):
+Code editor (e.g. VSCode):
+Vala Language Server (e.g. git commit, or PPA/AUR version):
+Vala version (`valac --version`):
+
+**To Reproduce**
+Source code repo:
+
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error