Add issue template

Author: 1st1

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,15 @@
+<!--
+Thanks for wanting to report an issue you've found in uvloop. Please fill in
+the template below.
+
+It will be much easier for us to fix the issue if a test case that reproduces
+the problem is provided, with clear instructions on how to run it.
+
+Thank you!
+-->
+
+* **uvloop version**:
+* **python version**:
+* **platform**:
+
+<!-- Enter your issue details below this comment. -->