Update document " Getting Started with MVP Site API"

[seiya1223]

If user have registered app for the old Live SDK(MSA applications) long time ago, they can see "Converged applications" section and "Live SDK applications" section. They can follow our current document to run our source code with the real MVP site API.
If user is a new developer for Live SDK, they cannot register the MSA applications but only can use the latest MSAL(We will support that in V2).