Add endpoint to retrieve random entry

[antonioalmeida]

At the moment only the entire document can be fetched, but retrieving a random entry would be way more interesting.

I'm leaving this issue open on purpose because it it quite simple and a beginner might try and have a go at it.

[enzomzaocv]

Hi, how it is going? I'll be glad to contribute, please assign this issue to me.

[antonioalmeida]

Go ahead @enzomzaocv , let me know if you need help. I'll try and development instructions tomorrow