cr_canseejailproc(9): New man page

Approved by: re (gjb)
Reviewed by: pauamma_gundo.com, mhorne
Sponsored by: Kumacom SAS
Differential Revision: https://reviews.freebsd.org/D40631

(cherry picked from commit 29d863bb7ffc692998f21fa3e7a91afa1151cf1c)
(cherry picked from commit 66eb6431479d1de3764228104ddd7a5f15ebf377)