Create page for documentation + reference to it on landing page

[B0r1sD]

The need for a public-facing documentation for usegalaxy.be has been there for a while, and it has been decided to do it here. Initially, one page containing different (sub)sections should do. Items to document should be collected here.

• Guide how to set up IGV with Galaxy input and local IGV install
• Daily container cache cleanup, which could be the reason why your first job could be a bit slower
• ...