docs: clarify training usage and signpost Discussions for feedback

[Liam Berrisford (liamjberrisford)]

Following Harley (@harley-kelly) suggestion ahead of the communications launch, I have added some brief usage guidance and links to GitHub Discussions in the README and course homepage. With more attention expected over the coming month, the idea is to help visitors get started and gives them a place to ask questions or share feedback without needing to open an issue or prepare a PR.

[Liam Berrisford (liamjberrisford)]

Harley (@harley-kelly) I’ve also added a welcome post and some guidance to Discussions to give it a little structure and a general framework for questions and feedback. Please feel free to change anything!

It might also be useful for someone with the appropriate repository permissions to use Announcements to highlight key messages, perhaps starting with the welcome post I created in General, as I don’t have permission to post announcements.

Happy to change any of the discussions stuff to whatever the MO had in mind but there is no PR mechanism there before making something go live and so tried to make it very general and follow what I have seen other repositories use.

[Harley (harley-kelly)]

Thanks Liam Berrisford (@liamjberrisford) looks great, will merge in now.