Added Some Resources (#7613)

* Added Some Resources

* remove trailing slash

* Sort alphatecially

* Removed Resource

courses/free-courses-en.md

@@ -108,6 +108,7 @@
 * [Codecademy](https://www.codecademy.com)
 * [Coursera](https://www.coursera.org)
 * [Datacamp](https://www.datacamp.com)
+* [DevDocs](https://devdocs.io)
 * [edX](https://www.edx.org)
 * [freeCodeCamp](https://www.freecodecamp.org)
 * [FutureLearn](https://www.futurelearn.com)