Add speaker notes to Android build rules (#2492)

Part of #1083.

src/android/build-rules/binary.md

@@ -24,3 +24,16 @@ You can now build, push, and run the binary:
 ```text
 Hello from Rust!
 ```
+
+<details>
+
+- Go through the build steps and demonstrate them running in your emulator.
+
+- Notice the extensive documentation comments? The Android build rules enforce
+  that all modules have documentation. Try removing it and see what error you
+  get.
+
+- Stress that the Rust build rules look like the other Soong rules. This is on
+  purpose to make it as easy to use Rust as C++ or Java.
+
+</details>

src/android/build-rules/library.md

@@ -38,3 +38,15 @@ You build, push, and run the binary like before:
 Hello Bob, it is very
 nice to meet you!
 ```
+
+<details>
+
+- Go through the build steps and demonstrate them running in your emulator.
+
+- A Rust crate named `greetings` must be built by a rule called `libgreetings`.
+  Note how the Rust code uses the crate name, as is normal in Rust.
+
+- Again, the build rules enforce that we add documentation comments to all
+  public items.
+
+</details>