Fix blog pagination and add contribute page

Created by: oyvkva

The numeric pagination on the blog page leads to https://getmonero.org/blog/page3/blog/page4/404 etc now, this has been fixed.

I saw all the views and answers this question got on Stack Exchange: http://monero.stackexchange.com/questions/1647/for-newcomers-to-the-monero-community-what-can-we-do-to-help-the-project

I was not able to find any place on the Monero website where this was explained so I made a page. I'm also a newcomer so please add or edit the content if needed. The content is mostly based on the answers to the question on Stack Exchange.