time range [beginning of day] - [beginning of next day] is needed for getStats() with StatAPI to get 1 day of data

[zcernigoj]

Mention that to get 1 day of statistical data with getStats() when StatAPI is used, you need to set time range to [beginning of day] - [beginning of next day] instead of [beginning of day] - [end of day] like for getMap(), getTiles(), ...

https://github.com/sentinel-hub/sentinelhub-js/blob/96c64b4f7c11a342776142c658a1005a2cee13b0/README.md?plain=1#L398