* Generate Markdown docs
This is largely copied from similar work in go-containerregistry
This required moving the Root command definition out of main() into a
place where it could be referenced from the gendoc tooling.
* fix boilerplate
* moar fix boilerplate
* update cmd/ko/main.go
* set -j to GOMAXPROCS at runtime
* rebase on cli-runtime change
* remove trailing whitespace
