Update contributing guidelines in README as we now have 100% mutant free coverage
Update contributing guidelines in README as we now have 100% mutant free coverage

mpraglowski/rails_event_store,RailsEventStore/rails_event_store,mpraglowski/rails_event_store,mpraglowski/rails_event_store,RailsEventStore/rails_event_store,mlomnicki/rails_event_store,mlomnicki/rails_event_store,RailsEventStore/rails_event_store,mpraglowski/rails_event_store,RailsEventStore/rails_event_store,arkency/rails_event_store,arkency/rails_event_store,arkency/rails_event_store,arkency/rails_event_store