Explicitly info user 1 stx address can only hold 1 BNS on btc.us homepage

Hi I'm seeing some cases where new people coming to Stacks assuming 1 address can hold multiple domains like on Ethereum can or other blockchains, but in fact Stacks currently cannot, and the landing page on btc.us does not highlight this enough imo, new users unknowingly attempt to buy multiple domains at once or one after another.

Can 1 address per BNS address be made super explicit on the homepage?
(I understand there are talks/or in works of having multiple BNS per address, however we can still have the 1 per address message live until improved feature comes)

Example of message not clear for user: https://discord.com/channels/621759717756370964/625538774230892545/968814415598211082

cc: @MarvinJanssen @friedger

Start at the btc.us homepage and identify where BNS purchase guidance is presented. Make the one-BNS-per-address limitation explicit for new users, then verify that the homepage clearly communicates this before users attempt to buy multiple domains.

Written by the indexing model from the issue text.