Write overview page for our activities

[gsambrotta]

This page is sub item of "About" section.
In this page we would like to give a overview about what we do and where we do it.
There will be two main sections:

1. OTS is worldwide: mention that we have chapters in different area of the world, explain how we approach OTS locally and globally
   Link to /chapters page

2. What we do: Explain we work with different format, we have different projects and we do lot of collaborations.
   Link to /projects page.
   (hint: http://www.opentechschool.org/projects/)