Add not about cacheCompression in the README

README.md

@@ -1,4 +1,4 @@
-> This readme is for babel-loader v8 + Babel v7  
+> This readme is for babel-loader v8 + Babel v7
 > Check the [7.x branch](https://github.com/babel/babel-loader/tree/7.x) for docs with Babel v6
 
 [![NPM Status](https://img.shields.io/npm/v/babel-loader.svg?style=flat)](https://www.npmjs.com/package/babel-loader)
@@ -88,7 +88,9 @@ This loader also supports the following loader-specific option:
 
 * `cacheIdentifier`: Default is a string composed by the babel-core's version, the babel-loader's version, the contents of .babelrc file if it exists and the value of the environment variable `BABEL_ENV` with a fallback to the `NODE_ENV` environment variable. This can be set to a custom value to force cache busting if the identifier changes.
 
-* `forceEnv`: Default will resolve BABEL_ENV then NODE_ENV. Allow you to override BABEL_ENV/NODE_ENV at the loader level. Useful for isomorphic applications with different babel configuration for client and server.
+* `cacheCompression`: Default `true`. When set, each Babel transform output will be compressed with Gzip. If you want to opt-out of cache compression, set it to `false` -- your project may benefit from this if it transpiles thousands of files.
+
+* `forceEnv`: Default will resolve `BABEL_ENV` then `NODE_ENV`. Allow you to override `BABEL_ENV`/`NODE_ENV` at the loader level. Useful for isomorphic applications with different babel configuration for client and server.
 
 __Note:__ The `sourceMap` option is ignored, instead sourceMaps are automatically enabled when webpack is configured to use them (via the `devtool` config option).