Make section on granting coin to the Validator to purchase traffic less confusing

[canton-network-da]

[ This issue was auto-migrated from DA's internal repo (DACH-NY/canton-network-node#18711). Original author: @martinflorian-da ]

Essentially, address this comment by @waynecollier-da :

global-synchronizer-foundation/docs#15 (comment)

Once merged:

• mention on the comment thread that we'll update the docs
• once the (GSF-hosted) docs have updated to consume the change: ask @waynecollier-da to perhaps hide the comment thread again