chore: added opencollective in the readme.md (#877)

README.md

@@ -8,7 +8,7 @@
 
 > A modular minifier, built on top of the [PostCSS](https://github.com/postcss/postcss) ecosystem.
 
-[![NPM version](https://img.shields.io/npm/v/cssnano.svg)](https://www.npmjs.org/package/cssnano)
+[![Backers on Open Collective](https://opencollective.com/cssnano/backers/badge.svg)](#backers) [![Sponsors on Open Collective](https://opencollective.com/cssnano/sponsors/badge.svg)](#sponsors) [![NPM version](https://img.shields.io/npm/v/cssnano.svg)](https://www.npmjs.org/package/cssnano)
 [![Build Status](https://dev.azure.com/cssnano/cssnano/_apis/build/status/cssnano.cssnano?branchName=master)](https://dev.azure.com/cssnano/cssnano/_build/latest?definitionId=3&branchName=master)
 [![codecov](https://codecov.io/gh/cssnano/cssnano/branch/master/graph/badge.svg)](https://codecov.io/gh/cssnano/cssnano)
 [![Gitter](https://img.shields.io/badge/Gitter-Join_the_PostCSS_chat-brightgreen.svg)](https://gitter.im/postcss/postcss)
@@ -40,6 +40,32 @@ You can now [try cssnano online](https://cssnano.co/playground/)!
 
 See [CONTRIBUTING.md](CONTRIBUTING.md).
 
+## Contributors
+
+This project exists thanks to all the people who contribute. [[Contribute](CONTRIBUTING.md)].
+<a href="https://github.com/cssnano/cssnano/graphs/contributors"><img src="https://opencollective.com/cssnano/contributors.svg?width=890&button=false" /></a>
+
+
+## Backers
+
+Thank you to all our backers! 🙏 [[Become a backer](https://opencollective.com/cssnano#backer)]
+
+<a href="https://opencollective.com/cssnano#backers" target="_blank"><img src="https://opencollective.com/cssnano/backers.svg?width=890"></a>
+## Sponsors
+Support this project by becoming a sponsor. Your logo will show up here with a link to your website. [[Become a sponsor](https://opencollective.com/cssnano#sponsor)]
+<a href="https://opencollective.com/cssnano/sponsor/0/website" target="_blank"><img src="https://opencollective.com/cssnano/sponsor/0/avatar.svg"></a>
+<a href="https://opencollective.com/cssnano/sponsor/1/website" target="_blank"><img src="https://opencollective.com/cssnano/sponsor/1/avatar.svg"></a>
+<a href="https://opencollective.com/cssnano/sponsor/2/website" target="_blank"><img src="https://opencollective.com/cssnano/sponsor/2/avatar.svg"></a>
+<a href="https://opencollective.com/cssnano/sponsor/3/website" target="_blank"><img src="https://opencollective.com/cssnano/sponsor/3/avatar.svg"></a>
+<a href="https://opencollective.com/cssnano/sponsor/4/website" target="_blank"><img src="https://opencollective.com/cssnano/sponsor/4/avatar.svg"></a>
+<a href="https://opencollective.com/cssnano/sponsor/5/website" target="_blank"><img src="https://opencollective.com/cssnano/sponsor/5/avatar.svg"></a>
+<a href="https://opencollective.com/cssnano/sponsor/6/website" target="_blank"><img src="https://opencollective.com/cssnano/sponsor/6/avatar.svg"></a>
+<a href="https://opencollective.com/cssnano/sponsor/7/website" target="_blank"><img src="https://opencollective.com/cssnano/sponsor/7/avatar.svg"></a>
+<a href="https://opencollective.com/cssnano/sponsor/8/website" target="_blank"><img src="https://opencollective.com/cssnano/sponsor/8/avatar.svg"></a>
+<a href="https://opencollective.com/cssnano/sponsor/9/website" target="_blank"><img src="https://opencollective.com/cssnano/sponsor/9/avatar.svg"></a>
+
+
+
 ## License
 
 MIT © [Ben Briggs](http://beneb.info)