Update README.md for Laravel UI

[jonathan-bird]

Description

This readme updates provides more details to someone overriding in Laravel UI.

Code samples

For example, in Laravel UI, a basic example in the LoginController would be:

protected function validateLogin(Request $request)
{
    // If the user is trying for the first time, ensure both email and the password are
    // required to log in. If it's not, then he would issue its 2FA code. This ensures
    // the credentials are not required again when is just issuing his 2FA code alone.
    if ($request->isNotFilled('2fa_code')) {
        $request->validate([
            'email' => 'required|email',
            'password' => 'required|string'
        ]);
    }
}

protected function attemptLogin(Request $request)
{
    return Auth2FA::attempt($this->credentials($request), $request->filled('remember'));
}

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[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (0e3949e) 99.75% compared to head (b175218) 99.75%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## 1.x #54 +/- ## ========================================= Coverage 99.75% 99.75% Complexity 140 140 ========================================= Files 18 18 Lines 408 408 ========================================= Hits 407 407 Misses 1 1 ```

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