docs: add readme for build/ (#10004)
docs: add readme for build/ (#10004)


umaar/lighthouse,ev1stensberg/lighthouse,ev1stensberg/lighthouse,wardpeet/lighthouse,GoogleChrome/lighthouse,ev1stensberg/lighthouse,GoogleChrome/lighthouse,wardpeet/lighthouse,wardpeet/lighthouse,ev1stensberg/lighthouse,GoogleChrome/lighthouse,GoogleChrome/lighthouse,GoogleChrome/lighthouse,umaar/lighthouse,wardpeet/lighthouse,wardpeet/lighthouse,umaar/lighthouse,umaar/lighthouse