look(1): Add EXAMPLES section

Add two simple examples. In this case I opted to show a small portion of
the output since it helps to understand what the tool does. It shows the use
of the -t flag too.

PR:
Submitted by:
Reported by:
Reviewed by: gbe@
Approved by: manpages (bcr@)
Obtained from:
MFC after:
MFH:
Relnotes:
Security:
Sponsored by:
Differential Revision: https://reviews.freebsd.org/D27543