cr_canseejailproc(9): New man page

Reviewed by: pauamma_gundo.com, mhorne
Sponsored by: Kumacom SAS
Differential Revision: https://reviews.freebsd.org/D40631

(cherry picked from commit 29d863bb7ffc692998f21fa3e7a91afa1151cf1c)

Approved by: markj (mentor)