Create code-bug.md (MystenLabs#2567)

.github/ISSUE_TEMPLATE/code-bug.md

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+---
+name: Sui Code Bug
+about: Create a new software bug for issues encountered running Sui
+title: 'Sui Code Bug or Feature Request'
+labels: bug
+assignees: ''
+---
+
+## Steps to Reproduce Issue
+
+Fill this in with the concrete steps needed to reproduce the bug. When providing code in the reproduction steps, use the smallest snippet of code that demonstrates the issue, removing any extraneous details.
+
+e.g.
+1. Call function <function call>.
+2. Use return value and call <other function call>.
+
+## Expected Result
+
+Specify what outcome you expected should have resulted, but didn't.
+
+e.g.
+Expected <other function call> to return 42.
+
+## Actual Result
+
+Specify what the actual unexpected outcome was.
+
+e.g.
+<other function call> returned 41.
+
+## System Information
+
+* OS: <specify OS version>
+* Compiler: <specify compiler version>