Update README with hints about package validation

README.md

@@ -26,6 +26,7 @@ The 3D Tiles validator can be used to validate 3D Tiles tilesets and their assoc
 - Validation of 3D Tiles Metadata
   - This includes the validation of the JSON structure of the metadata, as well as the structure and ranges of metadata values, both for the JSON based representation and for the binary metadata that is stored in property tables
 - A basic validation of the [`3DTILES_bounding_volume_S2` extension](https://github.com/CesiumGS/3d-tiles/tree/main/extensions/3DTILES_bounding_volume_S2)
+- Validation of tilesets that are contained in 3D Tiles package files (3ZT and 3DTILES files)
 
 ## Installation
 
@@ -42,6 +43,11 @@ npm install 3d-tiles-validator
 npx 3d-tiles-validator --tilesetFile specs/data/Samples/SparseImplicitQuadtree/tileset.json
 ```
 
+The input file can either be a tileset JSON file, or one of the known tileset package files. The known package file formats are 3TZ (a package format based on ZIP), and 3DTILES (a package format based on SQLite). The type of the input is determined from the file extension, which may be `.3tz` or `.3dtiles` (case-insensitively). For example, to validate a 3TZ file:
+```
+npx 3d-tiles-validator --tilesetFile ./specs/data/tilesets/packages/validTilesetPackage.3tz
+```
+
 #### Validate a set of tileset files
 ```
 npx 3d-tiles-validator --tilesetsDirectory specs/data/Samples/