fdp-primer: Add context instructions to two other locations and fix formatting
7dcf0bd6337554f7a57ca1fe4d1ef79a269a0a23 only changed the instructions on
how to add context to 'git format-patch' for Linux, leaving out the FreeBSD
and macOS sections. Add the same instructions there, too.
Additionally, I fixed the formatting of the enumerations I broke in the
commit mentioned above.
Event: Halifax Hackathon 202606
Location: Lying on the couch