Add create_asset_only_bundles.sh documentation in README.md

Author: dovix91

PlayAssetDelivery/BundletoolScriptSample/README.md

@@ -139,6 +139,28 @@ $ add_packs.py \
   --output ~/aug.aab
 ```
 
+### Generating Asset Only Bundles
+
+To generate an Android App Bundle containing only some asset packs, and no code, you should follow these steps:
+
+* build each asset pack individually with `generate_asset_pack.py`, like above
+* run `create_asset_only_bundle.sh` to package them into a bundle
+
+```
+$ sh create_asset_only_bundle.sh
+    --android-sdk=${HOME}/Android/Sdk
+    --bundletool=/google/bin/releases/bundletool/public/bundletool-all.jar
+    --output=output_directory/output_bundle.aab
+    --packdir=dir/containing/my/packs/
+    --packs=assetpack1,assetpack2
+    --tmpdir=/tmp/my-assetonly-tmp-dir/
+    --app-versions=10,12
+    --version-tag=mynewassets
+    [--ks=dir/to/keystore]
+    [--key=your-key]
+    [--ks_password=your-pw]
+```
+
 ## Misc
 
 ### Python Source File for App Bundle Config Proto
@@ -154,4 +176,4 @@ protobuf-compiler` and on macOS with [Macports](https://www.macports.org/) with:
 `$ sudo /opt/local/bin/port install protobuf3-cpp`
 
 Use the following command to regenerate `config_pb2.py` if required: `$ protoc
---python_out . config.proto`
+--python_out . config.proto`