[AssetMapper]: Adding possible precompressor values

Page: https://symfony.com/doc/current/frontend/asset_mapper.html#pre-compressing-assets

Info is taken from: https://symfony.com/blog/new-in-symfony-7-3-assets-pre-compression

Author: ThomasLandauer

frontend/asset_mapper.rst

@@ -768,6 +768,7 @@ and which file extensions should be compressed:
             # ...
 
             precompress:
+                # possible values: 'brotli', 'zstandard', 'gzip'
                 format: 'zstandard'
                 # if you don't define the following option, AssetMapper will compress all
                 # the extensions considered safe (css, js, json, svg, xml, ttf, otf, wasm, etc.)