Added docs

README.md

@@ -11,6 +11,9 @@ The following compression codings are supported:
 
   - deflate
   - gzip
+  - br (brotli)
+
+**Note** Brotli provides better and faster compression then gzip or deflate, but is supported only since Node.js versions v11.7.0 and v10.16.0.
 
 ## Install
 
@@ -46,6 +49,9 @@ as compressing will transform the body.
 those listed below, [zlib](http://nodejs.org/api/zlib.html) options may be
 passed in to the options object.
 
+As for *brotli*, a default is set to compression level 4, unless  
+[anything else is specified](https://nodejs.org/api/zlib.html#zlib_class_brotlioptions).
+
 ##### chunkSize
 
 The default value is `zlib.Z_DEFAULT_CHUNK`, or `16384`.