document missing or live doc server down

[leaveye]

as referenced by README.md

[flit]

Thanks for pointing this out.

Since CPM was moved to the pyocd org, the GitHub pages setup was broken and hasn't been fixed yet. Actually, the content was totally outdated, from before it moved to a Rust backend.

Fwiw, the cmsis-pack crate docs are here: https://docs.rs/cmsis-pack/0.2.0/cmsis_pack/