If I don’t define a default log component in a source file I get the following error:

src/mongo/logv2/log.h:66:2: error: #error "mongo/logv2/log.h requires MONGO_LOGV2_DEFAULT_COMPONENT to be defined. " "Please see http://www.mongodb.org/about/contributors/reference/server-logging-rules/ "

But the linked page was last edited in 2016. The guidance is outdated because it has been superseded by logv2. 

We should update the error message to include a link to an updated README about LOGV2.