Enhancement: Incorporate logging info from README

[vendillah]

Right now the login looks like this:

It neither doesn't warn the user that logging in through email is dangerous.

I'd like to suggest the following:

• display a link to README#Logging-In "how to get your token?" under the token login or perhaps these steps can be listed within the app.
• display the same warning message as in the README when the user is in the email tab: "Logging in using username/email and password is strongly discouraged. This method is untested and may cause your account to be banned! Prefer using the token method above."

I believe they are small changes, but useful for those who just installed dissent from flatpak and want to get started right away.