docs: add note about different compression effects in different browsers

ref #132

README.md

@@ -2,7 +2,7 @@
 
 [![Coverage Status](https://img.shields.io/codecov/c/github/fengyuanchen/compressorjs.svg)](https://codecov.io/gh/fengyuanchen/compressorjs) [![Downloads](https://img.shields.io/npm/dm/compressorjs.svg)](https://www.npmjs.com/package/compressorjs) [![Version](https://img.shields.io/npm/v/compressorjs.svg)](https://www.npmjs.com/package/compressorjs) [![Gzip Size](https://img.shields.io/bundlephobia/minzip/compressorjs.svg)](https://unpkg.com/compressorjs/dist/compressor.common.js) [![Dependencies](https://img.shields.io/david/fengyuanchen/compressorjs.svg)](https://www.npmjs.com/package/compressorjs)
 
-> JavaScript image compressor. Uses the Browser's native [canvas.toBlob](https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toBlob) API to do the compression work, which means it is **lossy compression** and **asynchronous**. General use this to precompress a client image file before upload it.
+> JavaScript image compressor. Uses the Browser's native [canvas.toBlob](https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toBlob) API to do the compression work, which means it is **lossy compression**, **asynchronous**, and has **different compression effects in different browsers**. General use this to precompress a client image file before upload it.
 
 - [Website](https://fengyuanchen.github.io/compressorjs)