split issue templates [skip ci]

.github/ISSUE_TEMPLATE/bug-report.md

@@ -0,0 +1,23 @@
+---
+name: Bug Report
+about: Report a problem with Chipyard
+labels: bug
+
+---
+
+<!-- choose one -->
+**Impact**: rtl | software | unknown | other
+
+**What is the current behavior?**
+
+**What is the expected behavior?**
+
+**Please tell us about your environment:**
+<!--    (examples)
+    - version: `chipyard git commit hash`
+    - os: `Linux knight 4.4.0-92-generic #115-Ubuntu SMP Thu Aug 10 09:04:33 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux`
+    - other: `prior steps taken/documentation followed/...`
+-->
+
+**Other information**
+<!-- include detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, ... -->