setup.sh automated build script issues: does not install `flutter` as expected, `cargo-ndk` fails to build

[AaronFeickert]

The build script does not properly install flutter, as this line fails.

It may also be the case that another source is needed after installing Rust.

[julian-CStack]

flutter version also needs to be updated in this script

[sneurlax]

Today on a new install I experienced this issue, where line 19 (flutter doctor) fails. Also, cargo-ndk failed to build. The documentation should be updated to note that Android Studio should be installed before the setup script it run, as well.