[v1-rest property/value] more descriptions

[beets]

Some nits:

• Can we add more description or examples to property
• For example 1: value should come first in the response example
• Example 2: an we add more description? And especially highlight in or out

[beets]

Re: value before provenance in the response, also in example 1 of https://juliawu.github.io/datacommons-docsite/api/rest/v1/triples