Expand on learning resources

[martinklepsch]

It would be nice if we collect more learning resources and catalog/link them on our website,

• https://aphyr.com/posts/301-clojure-from-the-ground-up-welcome

[nynnejc]

http://www.4clojure.com/

[Malwine]

I guess http://www.braveclojure.com/introduction/ is also an option.
We can add these links to the material section.

[Malwine]

We may not need to duplicate the links in both languages.

[Malwine]

The links above are resolved in the new material section. Pleas open a new issue for more links.