spell descriptions should mention system requirements

[mikemccracken]

Bug from LP via conjure-up/conjure-up#599

Note that this is probably true of all spells.

When I fire up conjure-up kubernetes I see two options:

Kubernetes Core
The Canonical Distribution of Kubernetes

There is actually a difference between them in terms of system requirements, but the description for either of them doesn't make it clear. Could we expose those so we know which option is suitable to select? We might want to surface more details (number of services, etc?) if that helps the choice.