makewhatis for man page changes

Hi All,

Turns out I don't know everything and I need to read man pages from
time-to-time. I'm sure you're like me and also want to consult the man pages.
How do you do it on applications you've installed from source?

Reading makewhatis.8, I think this is the tool I would use.

# makewhatis -D -a /usr/local/share/man
/usr/local/share/man//de/man1/nmap.1: Adding to database
/usr/local/share/man//es/man1/nmap.1: Adding to database
/usr/local/share/man//fr/man1/nmap.1: Adding to database
/usr/local/share/man//hr/man1/nmap.1: Adding to database
/usr/local/share/man//hu/man1/nmap.1: Adding to database
/usr/local/share/man//it/man1/nmap.1: Adding to database
/usr/local/share/man//ja/man1/nmap.1: Adding to database
/usr/local/share/man//man1/aerc.1: Adding to database
/usr/local/share/man//man1/curl-config.1: Adding to database
/usr/local/share/man//man1/curl.1: Adding to database
/usr/local/share/man//man1/dnscap.1: Adding to database
/usr/local/share/man//man1/enchive.1.gz: Adding to database
/usr/local/share/man//man1/endlessh.1: Adding to database
...

but this doesn't work:
$ man 1 nmap
man: No entry for nmap in section 1 of the manual.

What am I doing wrong?

Thanks for any tips!

$ sysctl kern.version
kern.version=OpenBSD 6.5-current (GENERIC.MP) #139: Wed Jul 24 05:11:28 MDT 2019
deraadt@amd64.openbsd.org:/usr/src/sys/arch/amd64/compile/GENERIC.MP