Add note about bluestore and how it can be mixed

See merge request !5

Add links to the main readme to point to design decisions

So they are visible from the front README of the project

See merge request !4

Add storage and networking documentation with our last agreements

This is what I mean, that instead of keeping the infrastructure documentation in the chef repo we can use the infrastructure repo which can be public.

We could just make it all public this way and keep the documents up to date by writing markdown and just using git.

cc/ @stanhu

See merge request !3

Add Git Blackbox monitoring url

See merge request !2

Add quick guide for system graphs

See merge request !1