add duration assertion example
add duration assertion example

playpasshq/ruby-jmeter,flood-io/ruby-jmeter,cyberw/ruby-jmeter,Ricardonacif/ruby-jmeter,cpalafox/ruby-jmeter,sworisbreathing/ruby-jmeter,vgvinay2/ruby-jmeter,irfanah/ruby-jmeter,rpocklin/ruby-jmeter,tacticiankerala/ruby-jmeter,JanStevens/ruby-jmeter