GitHub: add issue template for error messages

.github/ISSUE_TEMPLATE/error_message.yml

@@ -0,0 +1,26 @@
+name: Error message improvement
+description: Compiler produces an unhelpful or misleading error message.
+labels: ["error message"]
+body:
+  - type: input
+    id: version
+    attributes:
+      label: Zig Version
+      description: "The output of `zig version`"
+      placeholder: "0.11.0-dev.146+2897641fb"
+    validations:
+      required: true
+  - type: textarea
+    id: repro
+    attributes:
+      label: Steps to Reproduce and Observed Output
+      description: A complete list of steps to reproduce the error message.
+    validations:
+      required: true
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected Output
+      description: What information do expect the error message to include?
+    validations:
+      required: true