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>
Documentation: added missing word to 'library settings editor' docs

Added "editor" to label of what menu should be used.

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