README: updating to reflect new context segment features
README: updating to reflect new context segment features

rjorgenson/powerlevel9k,natemccurdy/powerlevel9k,shibumi/powerlevel9k,bhilburn/powerlevel9k,shibumi/powerlevel9k,dritter/powerlevel9k,natemccurdy/powerlevel9k,rjorgenson/powerlevel9k,bhilburn/powerlevel9k,dritter/powerlevel9k