Add example for Immutables+MapStruct

Ninguém assumiu esta issue ainda.

Would be nice to have an example that shows the usage of MapStruct with [Immutables](https://immutables.github.io/).

I was trying to use MapStruct with Immutables and couldn't find a comprehensive example or guide that could walk users through this set up. Would be nice to have this example.

I created a [sample](https://github.com/deepaks829/demo) Spring REST service that uses MapStruct and Immutables to post my [question](https://stackoverflow.com/questions/55888960/mapstruct-does-not-detect-setters-in-builder) on StackOverflow.

If you think this is a good addition, with some help and guidance I am willing to improve this to have it included as an example.

Nenhum arquivo do repositório ou teste é mencionado. Comece revisando os exemplos existentes em mapstruct-examples e o serviço REST Spring de demonstração vinculado; em seguida, compare a configuração de MapStruct e Immutables usada nele com as convenções do projeto. O trabalho estará concluído quando um exemplo abrangente ou um guia que demonstre a integração for adicionado.

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