Document what things "look like"

[jvoigtlaender]

I think what I would need as part of the public documentation:

• an example of a short Alloy specification
• how one of the AlloyInstances returned from a getInstances call for said specification could look like, as a (pretty-printed) Map Signature (Entry Map Set) value, at least partially given, with at least for one of the stored Entry Map Set values also shown what the annotation would be and at least sketched how the relation looks as a Map String (Relation Set)
• relevant scoped- and unscoped-calls for creating Signature values for the above instance
• examples of relevant getSingle, getDouble, getTriple calls along with their results for the above instance; so the example specification would have to be such that all three cases occur
• the possible cases/accessors for Objects

[marcellussiegburg]

Everything mentioned is covered by the README already.

@jvoigtlaender Feel free to reopen if you think there is still something missing