Update README.md (#5617)
Update README.md (#5617)

Include missing marathon-client for Java by Mesosphere.
meln1k/marathon,mesosphere/marathon,meln1k/marathon,meln1k/marathon,gsantovena/marathon,janisz/marathon,mesosphere/marathon,guenter/marathon,guenter/marathon,guenter/marathon,janisz/marathon,mesosphere/marathon,mesosphere/marathon,meln1k/marathon,gsantovena/marathon,gsantovena/marathon,janisz/marathon,janisz/marathon,gsantovena/marathon,meln1k/marathon,mesosphere/marathon,guenter/marathon,gsantovena/marathon,janisz/marathon,guenter/marathon