This adds a release note for all the SME support now in LLDB
and a page where I have documented the user experience (for want
of a better term) when using SVE and SME.
This includes things like which mode transitions can or cannot
be triggered from within LLDB. I hope this will serve to A: document
what I've implemented and B: be a user's guide to these extensions.
(though it is not a design document, read the commits and code
for that sort of detail)