Add Certificates

Hello Unicorn,

I've created [Awesome Certificates](https://github.com/PanxProject/awesome-certificates#readme)!

**The project's aim is to provide free computer science certifications & digital badges to earn.**

I have reviewed and commented on these PRs: [#2453](https://github.com/sindresorhus/awesome/pull/2453#issuecomment-1365686751), [#2418](https://github.com/sindresorhus/awesome/pull/2418#pullrequestreview-1230586435) and [#2394](https://github.com/sindresorhus/awesome/pull/2394#pullrequestreview-1230445990).

I've also followed the guidelines and checked project with `awesome-lint` with no issues detected. 

Looking forward to be awesome,
Thanks!

readme.md

@@ -651,6 +651,7 @@
 - [Product Management](https://github.com/dend/awesome-product-management#readme) - Learn how to be a better product manager.
 - [Roadmaps](https://github.com/liuchong/awesome-roadmaps#readme) - Gives you a clear route to improve your knowledge and skills.
 - [YouTubers](https://github.com/JoseDeFreitas/awesome-youtubers#readme) - Watch video tutorials from YouTubers that teach you about technology.
+- [Certificates](https://github.com/PanXProject/awesome-certificates#readme) - Free computer science certifications to showcase your knowledge.
 
 ## Security