docs(helper): Add documentation for Current Single Sign On Account LiveData in README.md

// If you stored the "default" account using setCurrentAccount(…) you can get the account by using the following line:

final var ssoAccount = SingleAccountHelper.getCurrentSingleSignOnAccount(context);

// It is also possible to get the "default" account as a LiveData object:

final var ssoAccount$ = SingleAccountHelper.getCurrentSingleSignOnAccount$(context);

// Otherwise (for multi-account support you'll have to keep track of the account names yourself. Note: this has to be the name of SingleSignOnAccount.name)

AccountImporter.getSingleSignOnAccount(context, accountName);