add rustup to requirements and a note about libhwloc-dev on linux

[44203]

just a couple of readme updates when setting up from scratch on ubuntu

[gmelodie]

Also why do we need rustup?

[44203]

Also why do we need rustup?

Unsure, but running make clean all fails if it isn't installed and asks for it.

[alvin-reyes]

Please move use dev as the upstream branch for this PR.