Expand issue template to encourage people to look at other resources first

While it is good for users to post issues, there are certain cases where we want to direct them to the discussions first, etc. We can expand the issue template to provide some extra guidance.

As an extreme example, here is spack's issue template:

Steps to reproduce the issue

$ spack install <spec>
...

Information on your system

Additional information

• spack-build-out.txt
• spack-build-env.txt

General information

• I have run spack debug report and reported the version of Spack/Python/Platform
• I have run spack maintainers <name-of-the-package> and @mentioned any maintainers
• I have uploaded the build log and environment files
• I have searched the issues of this repo and believe this is not a duplicate