Clarify Precision function in Timelion Kibana

[jaijhala]

There seems to be a confusion with how Precision function really works.

The description of .precision only says the data is rounded, but doesn't specify a direction, like rounded down (it does imply one by using the name "precision"). If we follow normal rounding rules, 0.99 would be rounded to 1 where 0.99 with a precision of 0 would be 0 as in 0.99 with no decimal places.

I think it would be good to clarify this maybe with an example as well or a note that the excess decimals are dropped or the number is "rounded down" to precision instead of just "rounded".

[lcawl]

I've created elastic/kibana#26100. If you have additional info or documentation links to contribute, please add them there!