Making CONTRIBUTING.md consistent across repos.
Making CONTRIBUTING.md consistent across repos.

vadimeisenbergibm/pilot,kyessenov/pilot,kyessenov/pilot,vadimeisenbergibm/pilot,istio/old_pilot_repo,vadimeisenbergibm/pilot,kyessenov/pilot,kyessenov/pilot,istio/old_pilot_repo,istio/old_pilot_repo