Merge pull request #2718 from sigiesec/issue-template

Problem: bug reports are often missing relevant information

.github/issue_template.md

+*Please use this template for reporting suspected bugs or requests for help.*
+
+# Issue description
+
+
+
+# Environment
+
+* libzmq version (commit hash if unreleased): 
+* OS: 
+
+# Minimal test code / Steps to reproduce the issue
+
+1.  
+
+
+# What's the actual result? (include assertion message & call stack if applicable)
+
+
+
+# What's the expected result?
+