Add flutter resource (#7902)

* Update free-programming-books-langs.md

* move

* Update free-courses-en.md

* Update free-courses-en.md

* Update free-courses-en.md

Co-authored-by: kalpesh <grimreaper12366@gmail.com>
Co-authored-by: Kalpesh <kalpesh.tated@jupiter.money>

courses/free-courses-en.md

@@ -553,6 +553,7 @@
 * [Flutter Tutorial](https://www.udacity.com/course/build-native-mobile-apps-with-flutter--ud905) - Matt Sullivan, James Williams, Mary Xia (Udacity)
 * [Flutter Tutorial for Beginners](https://www.udemy.com/course/learn-flutter-beginners-course) - Mayuresh Wankhede (Udemy)
 * [Flutter Tutorial for Beginners](https://www.youtube.com/playlist?list=PL4cUxeGkcC9jLYyp2Aoh6hcWuxFDX6PBJ) - The Net Ninja
+* [Flutter Tutorial for Beginners](https://www.solutelabs.com/blog/flutter-tutorial-for-beginners-step-by-step-guide) - Solute Labs
 * [Free Flutter Animations Course](https://youtube.com/playlist?list=PL4cUxeGkcC9gP1qg8yj-Jokef29VRCLt1) - The Net Ninja
 * [Free Flutter Course](https://www.youtube.com/playlist?list=PL6yRaaP0WPkVtoeNIGqILtRAgd3h2CNpT) - Vandad Nahavandipoor (YouTube)