atf-sh-api(3) doesn't mention atf-check(1)

[jmmv]

Originally filed by yaneurabeya at freebsd/kyua#98

atf-sh-api(3) mentions atf_check, but it doesn't reference atf-check(1), which could be helpful for folks getting started with atf.

[jmmv]

The tool and manpage are mentioned under the "Helper functions for common checks" section. Feel free to add the reference to "See also" as well.

[jmmv]

It does where atf_check is explained, but not in SEE ALSO.

The naming distinction between atf-check and atf_check is a bit unfortunate. Trying to run atf-check directly from test cases won't work because atf-check is installed in libexec, which is intended, so displaying the atf-check manpage more prominently would confuse users unless they also see the mention of atf_check.

If doing this, we'd need to change atf-check to clearly explain that it cannot be executed explicitly.

Another alternative would be to add a manpage for atf_check itself and maybe remove the one for atf-check.