Put system isolation feature square and Center

[rahuldave]

Proposed change

Rearrange some docs to put system isolation as a feature right up front. I missed this in multiple reads.

Who would use this feature?

Anyone wondering what tljh is for!

(Optional): Suggest a solution

The changes would be needed here: http://tljh.jupyter.org/en/latest/ (possibly), http://tljh.jupyter.org/en/latest/topic/whentouse.html#topic-whentouse , and here at https://github.com/jupyterhub/the-littlest-jupyterhub

[consideRatio]

Sorry for the late follow up on this @rahuldave! If you have time, could you try clarify what you referred to with system isolation a bit more clearly? I'm not sure what part you wanted to be more prominent when reading the docs.