fix(getting-started): fixes for the node/vs code download banners

[ChronosSF]

Closes #201

Main issues were:

• multiline anchor text is wrapped by p's by remark for mdx .This can be solved differently but in the interest of not complicating this, I preferred just fixing the block.
• the new design uses margin-bottom to add spaces between elements so we had to do that for the block too.