README: Add build instructions
README: Add build instructions

iAMr00t/gerrit-oauth-provider,kaija/gerrit-oauth-provider,TheNameIsNigel/gerrit-oauth-provider,netroby/gerrit-oauth-provider,mdxp/gerrit-oauth-provider,martincz/gerrit-oauth-provider,GerritCodeReview/gerrit-oauth-provider,dedalusdev/gerrit-oauth-provider