update language on contact index page


![image](https://f.cloud.github.com/assets/23801/1465879/c86e1dbe-4568-11e3-92ff-e6f218a55451.png)


this change:

* simplifies the first sentence
* moves the link to the help pages to the bottom, because data shows that few people
click on
* brings the description of the GOV.UK contact form closer in line with the User Support
team's actual remit