Documentation: Copied Stripe payment info into 'Library Settings Editor'

Only modified slightly from the documentation provided in the EG 2.6
release notes.

Signed-off-by: Yamil Suarez <yamil@yamil.com>
Documentation: Removed bare setting names from Stripe payment doc

Per jboyer-isl's suggestions

Signed-off-by: Yamil Suarez <yamil@yamil.com>