docs: expected goals and differences of various username, orgs/teams, and namespace registration systems

[moul]

There is a need to clarify the goals and differences of various username, orgs/teams, and namespace registrations in the Gno.land project, and how they can be independent or compete.

1. r/demo/users: This could remain as it is, a system with invite or paid registration, not an NFT, not transferable. This system could also become an example for other similar systems such as the r/demo/profile (WIP feat: initial r/profile dapp #181) that could allow configuring arbitrary data linked with an std.address that other apps could choose to use or not.

2. r/gnoland/names: This could be something with KYC or something different, independent from r/users. It would be used by the chain to filter “addpkg” calls so that you can only upload a realms in an allowed namespace, similar to github and personal/org limitations. See feat: add r/system/names #375.

3. r/demo/gns: This could be an ENS (ethereum) competitor which is basically an NFT, it could have a marketplace system and everything in a permissionless mode. See GNS (Gnoland Name Service) hackerspace#30.

[moul]

Update:

• r/demo/users will become the main and only official naming system. This system aims to create an ecosystem of social apps where usernames have meaning. It will likely be renamed to r/sys/users and linked with other contracts in the future, such as an auction contract and an anti-squatting contract. See r/sys/users Mainnet v1 (mvp) & v2 #2827.
• r/demo/profile allows for the configuration of extra fields, including a "display name." However, it is not intended to serve as a "username registry." Contract writers may want to import it to access richer information about users without requiring them to create a profile for each contract. Instead, this will centralize and keep their chain profile up to date. See feat: r/profile dapp #1983.
• There are currently no plans for r/demo/gns, but it may be developed at some point. While it’s not an issue if someone takes on this task, we need to establish r/demo/users as the official username system. This will help secure it over time and provide a trustworthy username system, which will directly impact the project's quality.