Update issue templates (xuperchain#2)

Add issue template

.github/ISSUE_TEMPLATE/xuperchain-issue-template.md

@@ -0,0 +1,26 @@
+---
+name: XuperChain Issue Template
+about: Describe this issue template's purpose here.
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Brief of the issue**
+Describe here
+
+**Your environment**
+XuperUnion and OS/Go/gcc version etc.
+
+**Repo steps**
+Describe how to reproduce this issue.
+
+**Expected behaviours**
+Describe what you expected to happen.
+
+**What actually happened**
+Describe what actually happened. Include the full traceback if there was an exception.
+
+**Additional information**
+If possible, include a minimal, complete, and verifiable example to help us identify the issue. This also helps check that the issue is not with your own code.