Make issue template a bit more welcoming

Author: killercup

.github/ISSUE_TEMPLATE.md

@@ -1,3 +1,11 @@
-assert_cli version
-rust version
-OS and version
+<!--
+Hi! If you want to report a bug, request a feature, or ask a question on how to
+use assert_cli, you have come to the right place!
+
+If you want to report a bug, please fill in the following. Otherwise, feel free
+to remove these lines.
+-->
+
+- `assert_cli` version:
+- Rust version:
+- OS and version: