doc(ffi): Add some doc comments for android_platform.rs

Author: jmartinesp

bindings/matrix-sdk-ffi/src/platform/android_platform.rs

@@ -6,9 +6,11 @@ use jni::{
 };
 use tracing::debug;
 
-pub(crate) static ANDROID_JVM: once_cell::sync::OnceCell<jni::JavaVM> =
-    once_cell::sync::OnceCell::new();
+static ANDROID_JVM: once_cell::sync::OnceCell<jni::JavaVM> = once_cell::sync::OnceCell::new();
 
+/// Initialize the platform support for Android targets.
+///
+/// This includes setting up `rustls-platform-verifier`.
 pub(crate) fn init() {
     debug!("Initializing Android platform support");
 
@@ -77,6 +79,7 @@ fn init_rustls_platform_verifier(env: &mut jni::JNIEnv<'_>) -> jni::errors::Resu
     Ok(rustls_platform_verifier::android::init_hosted(env, context)?)
 }
 
+/// Attach the current thread to a JVM one.
 pub(crate) fn android_attach_current_thread_permanently(
 ) -> jni::errors::Result<jni::JNIEnv<'static>> {
     ANDROID_JVM