update with dart sugestion (#6225)

* update with dart sugestion

* Update books/free-programming-books-pt_BR.md
Co-authored-by: NImVector <59611597+LuigiImVector@users.noreply.github.com>

* Update books/free-programming-books-pt_BR.md
Co-authored-by: NDavid Ordás <3125580+davorpa@users.noreply.github.com>

* Update books/free-programming-books-pt_BR.md
Co-authored-by: NDavid Ordás <3125580+davorpa@users.noreply.github.com>
Co-authored-by: NImVector <59611597+LuigiImVector@users.noreply.github.com>
Co-authored-by: NDavid Ordás <3125580+davorpa@users.noreply.github.com>

books/free-programming-books-pt_BR.md

@@ -9,6 +9,7 @@
 * [C](#c)
 * [C#](#c-sharp)
 * [C++](#cpp)
+* [Dart](#dart)
 * [Docker](#docker)
 * [Engenharia de software](#engenharia-de-software)
   * [Arquitetura de Software](#arquitetura-de-software)
@@ -108,6 +109,12 @@
 * [Programação Orientada a Objetos em C++](http://webserver2.tecgraf.puc-rio.br/~manuel/Download/Programacao%20Orientada%20a%20Objetos%20em%20C++.pdf) (PDF)
 
 
+### Dart
+
+* [Dart Documentação](https://dart.dev/guides) - dart.dev
+* [Flutter para Iniciantes](https://www.flutterparainiciantes.com.br) - Rubens de Melo (gitbook)
+
+
 ### Docker
 
 * [Descomplicando o Docker](https://livro.descomplicandodocker.com.br) - Jeferson Fernando