Add doc for tiup cluster env init (#4279)
Add doc for tiup cluster env init (#4279)

* Add doc for tiup cluster env init

Signed-off-by: lucklove <46500d655f5410ba7d8b9ea80b60e8a997057751@gmail.com>

* Apply suggestions from code review

Co-authored-by: TomShawn <3d0966147538bc5ab020e8dffa2c0b746f9728a6@users.noreply.github.com>
pingcap/docs-cn,pingcap/docs-cn