look: add page

[vitorhcl]

linux/look for #11827.

• The page(s) are in the correct platform directories: common, linux, osx, windows, sunos, android, etc.
• The page(s) have at most 8 examples.
• The page description(s) have links to documentation or a homepage.
• The page(s) follow the content guidelines.
• The PR title conforms to the recommended templates.

The command is available for Linux, FreeBSD, NetBSD, OpenBSD and macOS.

There are 4 differences between the implementations:

1. The flags -V/--version and -h/--help are only present on the util-linux version.
2. The flag -a/--alternative is only present on util-linux version (only FreeBSD version provides compatibility ignoring this flag)
3. On util-linux version -d/--alphanum search on blank and alphanumeric characters, whereas on the others the search is performed only on alphanumeric characters for historical reasons:

The original manual page stated that tabs and blank characters participated in comparisons when the -d option was specified. This was incorrect and the current man page matches the historic implementation.

4. util-linux, FreeBSD and macOS support long and short options, while NetBSD and OpenBSD only support short options.

[tldr-bot]

Hello! I've noticed something unusual when checking this PR:

• The page pages/freebsd/look.md already exists in the common directory.
• The page pages/linux/look.md already exists in the common directory.

Is this intended? If so, just ignore this comment. Otherwise, please double-check the commits.