[v1-rest variables] use better example

[beets]

https://juliawu.github.io/datacommons-docsite/api/rest/v1/variables

Can we use include an example for a place (of a different type) with much much more data? e.g. geoId/06, India, USA. Can use ellipses but if users try it out, they'll see how much data we have (and they will most likely just copy/paste the example).

[beets]

• I think it'll be helpful to add some more text (like with the linked examples or place info)
• It'll also be helpful to change the text of Example 1: get variables for an entity (and rename entity there to place or city).