Update getting-started.rst
Update getting-started.rst

Revised the instructions. Quickly get something running
mtakaki/metrics,timezra/metrics,mspiegel/metrics,tempredirect/metrics,ind9/metrics,chenxianghua2014/metrics,gburton1/metrics,wfxiang08/metrics,bentatham/metrics,cirrus-dev/metrics,ohr/metrics,egymgmbh/metrics,jplock/metrics,mnuessler/metrics,jasw/metrics,signalfx/metrics,mt0803/metrics,kevintvh/metrics,rexren/metrics,valery1707/dropwizard-metrics,ChetnaChaudhari/metrics,slovdahl/metrics,gburton1/metrics,unitsofmeasurement/metrics,AltitudeDigital/metrics,randomstatistic/metrics,mattnelson/metrics