Updating SELinux example doc in lininefile module

Encouraging users to use this Ansible module to enable SELinux seems
like a better idea. It also warms Dan Walsh's heart.

Signed-off-by: Major Hayden <major@mhtx.net>
Tweak docs to mention `replace`
Merge pull request #87 from offby1/devel

Tweak docs to mention `replace`
Merge pull request #77 from major/suggest-selinux-enforcing

Updating SELinux example doc in lininefile module