Update -etcd-endpoints command line option in README
Update -etcd-endpoints command line option in README

This patch updates the "key command line options" section in the README to reflect the changes regarding -etcd-endpoint(s) made in 74f9413deb00c0ca01bfb217aa56717b6edcfe64

lihuanghai/flannel,dcbw/flannel,jonboulle/flannel,bprashanth/flannel,coreos/flannel,lihuanghai/flannel,EverythingMe/flannel,MohdAhmad/flannel,svdata/flannel,adiclepcea/flannel,ingvagabund/flannel,bprashanth/flannel,lihuanghai/flannel,imzhulei/flannel,Yhgenomics/flannel,ingvagabund/flannel,flynn/flannel,MohdAhmad/flannel,sujitfulse/flannel,endocode/flannel,dcbw/flannel,eyakubovich/flannel,wikimedia/operations-debs-flannel,imzhulei/flannel,coreos/flannel,adiclepcea/flannel,svdata/flannel,eyakubovich/flannel,cusspvz/flannel,lvlv/flannel,flynn/flannel,MohdAhmad/flannel,kelcecil/flannel,kelcecil/flannel,jonboulle/flannel,jonboulle/flannel,wikimedia/operations-debs-flannel,benbjohnson/flannel,benbjohnson/flannel,ingvagabund/flannel,coreos/flannel,lvlv/flannel,cusspvz/flannel,flynn/flannel,wikimedia/operations-debs-flannel,benbjohnson/flannel,adiclepcea/flannel,kelcecil/flannel,eyakubovich/flannel,endocode/flannel,sujitfulse/flannel,EverythingMe/flannel,dcbw/flannel,cusspvz/flannel,imzhulei/flannel,bprashanth/flannel,sujitfulse/flannel,endocode/flannel,svdata/flannel,Yhgenomics/flannel,lvlv/flannel,EverythingMe/flannel,Yhgenomics/flannel