README: point developers to GerritHub
README: point developers to GerritHub

Kitoon uses GerritHub for changes, not GitHub PRs.

Change-Id: I7f8547a7bfc0e28c98713f301e638428e8892dff
Signed-off-by: Ken Dreyer <940dddfbf8b0685439b7ecf27daa0ba58b359a2c@redhat.com>

cloudbehl/tendrl_frontend,skyrings/kitoon,Tendrl/dashboard,kmkanagaraj/usm-client-2,kmkanagaraj/usm-client-2,skyrings/kitoon,kmkanagaraj/usm-client-2,cloudbehl/tendrl_frontend,Tendrl/dashboard,skyrings/kitoon