Merge "GD Rust: Update README.md"

You should use `build.py` at the root to do your Rust builds so that it

correctly points your dependencies towards the vendored crates and sets your

$CARGO_HOME to the correct location.

### Building `packets` package

This package depends on `bluetooth_packetgen` and thus simply using

`cargo build` will fail. Follow the steps below to ensure the dependency is

found in `$CARGO_HOME/bin`.

1. Run `m -j32 bluetooth_packetgen` to compile `bluetooth_packetgen` c++ binary.

2. Change directory to `$CARGO_HOME/bin`.

3. Create a symlink in `$CARGO_HOME/bin` to compiled `bluetooth_packetgen`.

`ln -s ~/aosp/out/host/linux-x86/bin/bluetooth_packetgen bluetooth_packetgen`

### Enable GD Rust

1. `adb shell device_config put bluetooth INIT_gd_rust true`

2. Restart the device