Update README.md
Added more to the readme and organized its content
Merge branch 'master' into dev
Fixed the times on two shifts
Added liable field to workshift instance, when people sign out too late
Added verify_cutoff field to WorkshiftPool
make_instances takes now as an optional argument to override the day to start from
collect_blown uses .liable and .verify_cutoff now
Separated out past_verify and past_sign_out for use in other modules
Added more checks to shift interactions
Don't show verify button after its cutoff
Fixed and updated the utils tests
Added django-cron to regularly mark shifts as blown / closed