Update description of tabs

[caredg]

cms-opendata-guide/docs/index.md

Line 10 in a6a673e

There are three main tabs to help you navigate the site. It starts with the **Computing Tools** most likely needed to deal with CMS open data. Then, there is a little review of **CMSSW**, which is the software used by CMS. Finally the **Analysis** section guides you through the different steps (in the most general order) that you need to follow for performing a particle physics analysis with CMS open data.

This gets outdated if someone adds a section tab. Maybe it can be rewritten to make it more general and avoid having to update it every time something changes