Reference Issues/PRs

closes #32680

What does this implement/fix? Explain your changes.

Thanks for your input on #32680 .

I've amended the Issues for New Contributors section to:

• recommend that people start somewhere that interests them or they are already familiar with
• advised that we rarely use the 'Good first issue' label
• advise them to start by reading the contributing guide. I've highlighted particular sections, as our contributing guide is very long, but not sure if I've included the right/best sections.

Note - I agree with @lesteve's sentiment here: #32343 (comment), in that our contributing page contains a lot of different topics and could do with a clean up. This PR works within the way the current doc is.

Any other comments?