Update issue templates

Initial issue template. Created following https://help.github.com/en/github/building-a-strong-community/configuring-issue-templates-for-your-repository#configuring-the-template-chooser. 

If change is needed, we could go another round.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,34 @@
+---
+name: Bug report
+about: Create a report to help us improve our code.
+title: "[BUG] "
+labels: bug
+assignees: ''
+
+---
+
+**Describe the bug**
+A concise description of what the bug is.
+
+**Target**
+- Development board: [e.g. HiFive11 RevB]
+- Instruction Set Architecture: [e.g. RV32IMAC]
+- IDE and version: [e.g. Freedom Studio 4.12.0.2019-08-2]
+- Toolchain and version: [e.g. riscv64-unknown-elf-gcc-8.3.0-2019.08.0]
+
+**Host**
+- Host OS: [e.g. MacOS]
+- Version: [e.g. Mojave 10.14.6]
+
+**To Reproduce**
+- Use project ... and configure with ...
+- Run on ... and could observe ... 
+
+**Expected behavior**
+A concise description of what you expected to happen.
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**Additional context**
+Add any other context about the problem here.