Example data - link to in docs, and clear up language

[odscjames]

• There is the page http://docs.openreferral.org/en/latest/hsds/sample_data/ but it's not in the menu and the content will need updating.
• Samples & examples is used inconsistently; standardise on example.

Broken out from https://github.com/openreferral/specification/pull/255

[mrshll1001]

Closing as the sample_data page is no longer part of the docs. We can open up a new ticket if we want to add a new/updated version of this in.