Update median doc to note return value of even-sized input (#44562)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44562
Add a note that torch.median returns the smaller of the two middle elements for even-sized input and refer user to torch.quantile for the mean of the middle values.
fixes https://github.com/pytorch/pytorch/issues/39520
Test Plan: Imported from OSS
Reviewed By: albanD
Differential Revision: D23657208
Pulled By: heitorschueroff
fbshipit-source-id: 2747aa652d1e7f10229d9299b089295aeae092c2
