address more comments

pkgs/native_assets_builder/doc/protocol/v1.md

@@ -10,6 +10,8 @@ A reference to a file that is identified by an `assetId`. There may be multiple
 same `assetId` with different characteristics such as `target` or `link_mode`.
 
 Note that in v1 there are _only_ native code assets, no data assets.
+Native code assets are dynamic libraries.
+Native data assets will be blobs of data accessible as a byte list in Dart.
 
 #### AssetId
 An asset must have an `assetId`. Dart code that uses an asset, references the
@@ -33,8 +35,8 @@ Dart and Flutter SDKs to be specified below:
 
 
 ### `build.dart`
-A package with native assets MUST define a `build.dart` file which accepts
-a `--config` option as follows:
+To bundle native assets with a package, that package must define a `build.dart`
+script which accepts a `--config` option as follows:
 
 ```console
 $ dart build.dart --config <build_config.yaml>
@@ -61,7 +63,8 @@ The `build.dart` file MUST:
 
 
 ### `build_config.yaml`
-Configuration file passed to `build.dart` as the `--config` option.
+The Dart and Flutter SDK invoke `build.dart` of all packages in the transitive
+dependencies and pass a `build_config.yaml` as the `--config` option.
 
 ```yaml
 # Build in dry-run mode.