Comment out template guidelines

Thanks @vors! This makes the guidelines not show up in the rendered
issue/pull request, but keeps the text in the source.

.github/ISSUE_TEMPLATE.md

@@ -1,9 +1,11 @@
+<!--
 Before submitting this issue, please first:
 
 - [ ] Search the existing issues.
 - [ ] Refer to the [FAQ](../docs/FAQ.md).
 - [ ] Refer to the [known issues](../docs/KNOWNISSUES.md).
 - [ ] If it is a bug, fill out this form:
+-->
 
 Steps to reproduce
 ------------------
@@ -20,7 +22,7 @@ Actual behavior
 Environment data
 ----------------
 
-Please fill in the results of the following commands:
+<!-- Please fill in the results of the following commands: -->
 
 ```sh
 $ dotnet --info