Fixed headless documentation
Fixed headless documentation

– Chromium package and executable are named ```chromium-browser``` in Ubuntu 16.04. 
– setting $DISPLAY seems not to be required
– chromium has a --temp-profile flag that seems to do the same previously done manually
wardpeet/lighthouse,ev1stensberg/lighthouse,GoogleChrome/lighthouse,deepanjanroy/lighthouse,tommycli/lighthouse,ev1stensberg/lighthouse,wardpeet/lighthouse,wardpeet/lighthouse,deepanjanroy/lighthouse,umaar/lighthouse,umaar/lighthouse,arturmiz/lighthouse,ev1stensberg/lighthouse,tommycli/lighthouse,GoogleChrome/lighthouse,wardpeet/lighthouse,umaar/lighthouse,deepanjanroy/lighthouse,cedricbellet/lighthouse,deepanjanroy/lighthouse,mixed/lighthouse,cedricbellet/lighthouse,deepanjanroy/lighthouse,tkadlec/lighthouse,GoogleChrome/lighthouse,GoogleChrome/lighthouse,wardpeet/lighthouse,cedricbellet/lighthouse,tkadlec/lighthouse,arturmiz/lighthouse,mixed/lighthouse,tommycli/lighthouse,umaar/lighthouse,tommycli/lighthouse,arturmiz/lighthouse,arturmiz/lighthouse,cedricbellet/lighthouse,GoogleChrome/lighthouse,mixed/lighthouse,mixed/lighthouse,tommycli/lighthouse,tkadlec/lighthouse,cedricbellet/lighthouse,ev1stensberg/lighthouse,tkadlec/lighthouse,arturmiz/lighthouse