update timeline in README
update timeline in README

codeforamerica/somerville-teacher-tool,codeforamerica/somerville-teacher-tool,studentinsights/studentinsights,codeforamerica/somerville-teacher-tool,erose/studentinsights,studentinsights/studentinsights,studentinsights/studentinsights,jhilde/studentinsights,jamestyack/somerville-teacher-tool,erose/studentinsights,jamestyack/somerville-teacher-tool,erose/studentinsights,hunterowens/somerville-teacher-tool,jhilde/studentinsights,jhilde/studentinsights,erose/studentinsights,hunterowens/somerville-teacher-tool,hunterowens/somerville-teacher-tool,jamestyack/somerville-teacher-tool,studentinsights/studentinsights,codeforamerica/somerville-teacher-tool,jhilde/studentinsights