README: Add credits to zenorocha/clipboard.js (MIT License)

@iBug really wants a place here in the Credits section :P

README.md

@@ -135,7 +135,7 @@ To install:
 
 For detailed instructions on how to configure, customize, add/migrate content, and more read the [theme's documentation](https://mmistakes.github.io/minimal-mistakes/docs/quick-start-guide/).
 
----
+------
 
 ## Contributing
 
@@ -159,7 +159,7 @@ To set up your environment to develop this theme, run `bundle install`.
 
 To test the theme, run `bundle exec rake preview` and open your browser at `http://localhost:4000/test/`. This starts a Jekyll server using content in the `test/` directory. As modifications are made to the theme and test site, it will regenerate and you should see the changes in the browser after a refresh.
 
----
+------
 
 ## Credits
 
@@ -190,8 +190,9 @@ To test the theme, run `bundle exec rake preview` and open your browser at `http
 - [Gumshoe](https://github.com/cferdinandi/gumshoe)
 - [jQuery throttle / debounce](http://benalman.com/projects/jquery-throttle-debounce-plugin/)
 - [Lunr](http://lunrjs.com)
+- [Clipboard.js](https://clipboardjs.com)
 
----
+------
 
 ## License
 
@@ -270,3 +271,7 @@ Pure Liquid Jekyll Table of Contents is distributed under the terms of the [MIT
 Minimal Mistakes incorporates [Lunr](http://lunrjs.com),
 Copyright (c) 2018 Oliver Nightingale.
 Lunr is distributed under the terms of the [MIT License](http://opensource.org/licenses/MIT).
+
+Minimal Mistakes incorporates [clipboard.js](https://clipboardjs.com/),
+Copyright (c) 2021 Zeno Rocha.
+Clipboard.js is distributed under the terms of the [MIT License](https://opensource.org/licenses/MIT).