add descriptions to service type list

[ccheetham]

For example, change

% steeltoe list-service-types
config-server
service-registry

to

% steeltoe list-service-types
config-server (Spring Cloud Config Server)
service-registry (Netflix Eureka Server)

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/159970791

The labels on this github issue will be updated when the story is started.