Added whereLocale and whereLocales methods

[ahmetbarut]

In some cases, there are times when I want to extract content according to the user's locale, and in this case, I found these solutions instead of constantly writing queries.

whereLocale and whereLocales methods.

$post->whereLocale('title', 'en')->get();

// or mutliple locales
$post->whereLocales('title', ['en', 'fr'])->get();

[freekmurze]

Thanks, could you also mention these in the readme with a good example.

[ahmetbarut]

@freekmurze I have attached documentation for both this pull request and the previous pull request

[freekmurze]

Thanks!