Docs/add question template (#310)

* docs: add issue template for question.

* add template summary

* reflect review

.github/ISSUE_TEMPLATE/QUESTION.md

@@ -0,0 +1,19 @@
+---
+name: ❓ Support Question
+about: Not sure how something works or how to implement some functionality? Ask us here! (But please check the README or issues first 🙃)
+---
+
+### Question Checklist
+
+- [ ] Updated grpc-swift to the latest version
+- [ ] I read the [Contribution Guidelines](https://github.com/grpc/grpc-swift/blob/master/CONTRIBUTING.md)
+- [ ] I read [README](https://github.com/grpc/grpc-swift/blob/master/README.md)
+- [ ] I searched for [existing GitHub issues](https://github.com/grpc/grpc-swift/issues) (especially, there are many [resolved issues related to SSL](https://github.com/grpc/grpc-swift/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aclosed+ssl))
+
+### Question Subject
+<!-- Is this a question about documentation? -->
+<!-- Is this a question about a third party plugin? (If so, please go to the plugin repository first) -->
+
+#### Question Description
+<!-- Please include expected behavior and any relevant code samples with your question if possible -->
+<!-- Please wrap log statements and code in triple backticks (```) so they get printed correctly on GitHub. -->