Add archived gatewayd.md
Add archived gatewayd.md

original: https://github.com/ripple/ripple-dev-portal/blob/7d64a79a985b9a06a423338dcc0905eea2fc0ee4/content/gatewayd.md
zealord/gatewayd,whotooktwarden/gatewayd,zealord/gatewayd,whotooktwarden/gatewayd