Some Android and MCU doc (#5286)

MCU: Add missing info for software renderer
Android: Add some more details for dev env setup

api/rs/slint/android.rs

@@ -46,19 +46,35 @@
 //!
 //! ## Building and Deploying
 //!
+//! Building a Rust application requires the target toolchain to be installed. You can install it via `rustup`. For example, to target AArch64 Android, use the following command:
+//!
+//! ```sh
+//! rustup target add aarch64-linux-android
+//! ```
+//!
+//! Make sure that you have the Android NDK and SDK installed and set up in your development environment.
+//! For detailed instructions on how to set up the Android NDK and SDK, please refer to the [Android Developer's guide](https://developer.android.com/studio/projects/install-ndk).
+//! The following environment variables need to be set:
+//! * `ANDROID_HOME`: The directory in which your Android SDK is located. Usually `$HOME/Android/Sdk`.
+//! * `ANDROID_NDK_ROOT`: The directory in which your Android NDK is located. Usually `$HOME/Android/Sdk/ndk/${NDK_VERSION}`. ${NDK_VERSION} is the version of the NDK you have installed.
+//! * `JAVA_HOME`: The directory in which your Java compiler (`javac`) is located. This variable is optional if a `javac` is found in your `$PATH`. 
+//!   Otherwise you can set `JAVA_HOME` to the `javac` installation shipped with Android Studio in `android-studio/jbr`.
+//!
 //! To build and deploy your application, we suggest the usage of [cargo-apk](https://github.com/rust-mobile/cargo-apk),
 //! a cargo subcommand that allows you to build, sign, and deploy Android APKs made in Rust.
 //!
 //! You can install it and use it with the following command:
 //!
 //! ```sh
 //! cargo install cargo-apk
+//! ```
+//!  
+//! Build and run your application with the following command:
+//!
+//! ```sh
 //! cargo apk run --target aarch64-linux-android --lib
 //! ```
 //!
-//! Please ensure that you have the Android NDK and SDK installed and properly set up in your development environment for the above command to work as expected.
-//! For detailed instructions on how to set up the Android NDK and SDK, please refer to the [Android Developer's guide](https://developer.android.com/studio/projects/install-ndk).
-//! The `ANDROID_HOME` and `ANDROID_NDK_ROOT` environment variable need to be set to the right path.
 //!
 //! Note Slint does not require a specific build tool and can work with others, such as [xbuild](https://github.com/rust-mobile/xbuild).
 

api/rs/slint/mcu.md

@@ -29,7 +29,7 @@ Start by adding a dependency to the `slint` and the `slint-build` crates to your
 Start with the `slint` crate like this:
 
 ```sh
-cargo add slint@1.6.0 --no-default-features --features "compat-1-2 unsafe-single-threaded libm"
+cargo add slint@1.6.0 --no-default-features --features "compat-1-2 unsafe-single-threaded libm renderer-software"
 ```
 
 The default features of the `slint` crate are tailored towards hosted environments and includes the "std" feature. In bare metal environments,
@@ -43,6 +43,7 @@ In the snippet above, three features are selected:
    feature changes Slint to use unsafe static for storage. This way, you guarantee to use Slint API only from a single thread, and not from interrupt handlers.
  * `libm`: We select this feature to enable the use of the [libm](https://crates.io/crates/libm) crate to provide traits and functions for floating point arithmetic.
    They're typically provided by the Rust Standard Library (std), but that's not available in bare metal environments.
+ * `renderer-software`: We select this feature to use Slint's built-in software renderer. 
 
 It might be necessary to enable the [Feature resolver version 2](https://doc.rust-lang.org/cargo/reference/features.html#feature-resolver-version-2)
 in your Cargo.toml if you notice that your dependencies are attempting to build with `std` support even when disabled.