Add 'getting help' section to 'Getting Started with Qt'

Add a 'getting help' section to 'Getting Started with Qt. In the section we can link to the forum, and Qt Support. We should also mention that you get limited installation support for evaluation users.

'Getting Started with Qt' is our landing page for new users. Anyhow, it seems quite some customers struggle within the process (either at the installation phase, or further on). We should make it obvious to them were they can get help. For open source users this is the forum. For commercial users this is primarily the support in the Qt Account.