uuidgen: add page

[sparkchaser]

• The page (if new), does not already exist in the repo.
• The page is in the correct platform folder (common/, linux/, etc.)
• The page has 8 or fewer examples.
• The PR title conforms to the recommended templates.
• The page follows the content guidelines.

Part of the list in #2214

[agnivade]

I don't seem to have this option on Ubuntu 16.04.

Usage:
 uuidgen [options]

Create a new UUID value.

Options:
 -r, --random     generate random-based uuid
 -t, --time       generate time-based uuid
 -V, --version    output version information and exit
 -h, --help       display this help and exit

[sbrl]

It exists on 18.04.