Rollup of 8 pull requests#73977

Merged

bors merged 20 commits intorust-lang:masterfrom

Manishearth:rollup-2x4s7c6

Jul 3, 2020

Commits on Jun 17, 2020

move contributing.md to rustc-dev-guide and point at getting started
mark-i-m
committed

Commits on Jun 26, 2020

Update psm version
nagisa
committed

Commits on Jul 2, 2020