Add issue templates to zstd

LZ4 just added this. I think it would be helpful here too.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,35 @@
+---
+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.
+
+**To Reproduce**
+Steps to reproduce the behavior:
+1. Downloads data '...'
+2. Run '...' with flags '...'
+3. Scroll up on the log to '....'
+4. See error
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Screenshots and charts**
+If applicable, add screenshots and charts to help explain your problem.
+
+**Desktop (please complete the following information):**
+ - OS: [e.g. Mac]
+ - Version [e.g. 22]
+ - Compiler [e.g gcc]
+ - Flags [e.g O2]
+ - Other relevant hardware specs [e.g. Dual-core]
+ - Build system [e.g. Makefile]
+
+**Additional context**
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,20 @@
+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**Describe the solution you'd like**
+A clear and concise description of what you want to happen.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.