Installation page needs attention

Came across this link that need to be adjusted and made nicer:

https://about.gitlab.com/installation/

For sure, right now it is looking a bit broken (must be a recent bug). /cc @JobV

pushed a quick fix that makes it look not-broken.

Thanks @JobV

mentioned in merge request !552 (merged)

Reassigned to @sabbap

Status changed to closed by commit 7503749e

mentioned in commit 7503749e