Add git logo to README
Add git logo to README

Recognizable logo in many places
MarkEWaite/git-plugin,jenkinsci/git-plugin,martinda/git-plugin,v1v/git-plugin,MarkEWaite/git-plugin,MarkEWaite/git-plugin,MarkEWaite/git-plugin,jenkinsci/git-plugin,v1v/git-plugin,martinda/git-plugin,v1v/git-plugin,jenkinsci/git-plugin,jenkinsci/git-plugin,martinda/git-plugin