add docs for public flag on jobs
add docs for public flag on jobs

[finishes #79797096]

cjcjameson/concourse,concourse/concourse,longnguyen11288/concourse,sedouard/concourse,squeedee/concourse,jbayer/concourse,beni55/concourse,Amit-PivotalLabs/concourse,concourse/concourse,longnguyen11288/concourse,concourse/concourse,concourse/concourse,zachgersh/concourse,holgero/concourse,beni55/concourse,zachgersh/concourse,concourse/concourse,jbayer/concourse,holgero/concourse,CloudCredo/concourse,squeedee/concourse,cjcjameson/concourse,zachgersh/concourse,sedouard/concourse,jbayer/concourse,squeedee/concourse,longnguyen11288/concourse,CloudCredo/concourse,sedouard/concourse,cjcjameson/concourse,beni55/concourse,Amit-PivotalLabs/concourse,CloudCredo/concourse,holgero/concourse,Amit-PivotalLabs/concourse