Update source/getting_started.textile

Light typo edits
[ubuntu-deploy] Must include spree assets within static assets block in nginx config
Shipping category impact on ship method.
Remove default_locale references from preferences guide
Fix broken link for coupons and discounts

Fixes #81
Update guide for deployment service to require proper Linux distro (Ubuntu 12.04 LTS).

There were discrepancies between the guide and deployment service page; this commit simply updates the outdated text.

Fixes #82