Add speaker notes to AIDL slide (#2494)

Part of #1083.

Author: mgeisler

src/android/aidl.md

@@ -7,3 +7,12 @@ Rust:
 
 - Rust code can call existing AIDL servers,
 - You can create new AIDL servers in Rust.
+
+<details>
+
+- AIDL is what enables Android apps to interact with each other.
+
+- Since Rust is supported as a first-class citizen in this ecosystem, Rust
+  services can be called by any other process on the phone.
+
+</details>