[1.9] clearify description of xss security settings (#1566)
[1.9] clearify description of xss security settings (#1566)

* clearify description of xss security settings

* fix typo

Co-Authored-By: Rotzbua <7b8ebe1d366a4e4e00d63f8ce6eabeaba4ffb592@users.noreply.github.com>

getgrav/grav-plugin-admin,getgrav/grav-plugin-admin,getgrav/grav-plugin-admin