[Docs] add js-extra link to complementary-tools section

[alexandre-lelain]

Hello!

First of all, many thanks to the contributor of Lodash, which is a library I use on a daily basis.

What this PR does

It adds a link to js-extra in the Complementary tools section of the main page. It is an open source library that aims to complement lodash by providing a set of few specific functions we often duplicate across applications.

I feel like it solves quite recurrent problems, that is why I'm suggesting to add it. If you think it is not suitable enough, I would totally understand.

[jsf-clabot]

All committers have signed the CLA.