Update readme with links to service guides

- Add links to service specific pattern libraries for Apprenticeships,
Rural Payments and Land Registry.
Merge pull request #39 from alphagov/add-links-to-service-guides

Update readme with links to service guides
hotfix: Add display:block to #page-container

This was accidentally removed when the new grid includes were added.
hotfix: Remove ignore-for-ie var

This was preventing content being center aligned in IE8 and below
Fix broken skiplink

This should now link to #page-container, the page content wrapper.
Revert "Revert "Merge pull request #40 from alphagov/add-placeholder-support""

This reverts commit f8de27fd6fbb442ceabea11072efba4c4c9d7b74.