Update README.md

Author: AUdaltsova

ocf_datapipes/load/README.md

@@ -48,4 +48,5 @@ Add sanity checks to ensure time is unique and monotonic
 Current tests include:
     - checking the loaded data is not None
     - checking all expected dimensions are present
+    - (for some data) checking returns a xr.DataArray
 4. Calculate the mean and std of your data and add to `ocf_datapipes/utils/consts.py`