Rock the JVM + learning links

[daniel-ciocirlan]

cc @djspiewak

Added learning links for Rock the JVM's Cats course to the docs website + fixed a minor display issue with the learner resources page.

For context: I run this website called Rock the JVM which creates free and paid learning material on all major tools in the Scala ecosystem. This Cats course has been live since mid-2020 with overwhelmingly positive feedback. I think the course would benefit many more people if only they knew it existed, hence this PR.

Happy to help with any info!