Create command-reference.md (#445)

Fixes https://github.com/apple/container/issues/375

.github/pull_request_template.md

@@ -0,0 +1,17 @@
+## Type of Change
+- [ ] Bug fix
+- [ ] New feature  
+- [ ] Breaking change
+- [ ] Documentation update
+
+## Description
+[Brief description]
+
+## Motivation and Context
+[Why is this change needed?]
+
+## Testing
+- [ ] Tested locally
+- [ ] Added/updated tests
+- [ ] Added/updated docs
+