Add a fortune describing how to upload a machine's dmesg information to the
NYCBUG database.

We want to encourage our users to upload their dmesgs so that the project can
get a better insight into what kind of hardware is run on. This helps in making
data-driven decisions about i.e., platform and driver support.

Note that dmesgs may contain sensitive information like hardware serial numbers,
hence uploading them without review is discouraged.

Reviewed by: brooks, imp, allanjude
Approved by: allanjude
MFC after: 5 days
Differential Revision: https://reviews.freebsd.org/D17705