The first to point this out, in February 2020, was the Wuhan Institute of Virology:
https://link.springer.com/content/pdf/10.1007/s12250-020-002...
This strange furin cleave site allows the virus to bind to human ACE2 receptors. An interesting scientific reading on this, which does not rule out genetic manipulation in a lab:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/bies.2020002...
https://www.sciencedirect.com/science/article/pii/S187350612...
HCoV-OC43 and HCoV-UK1 both have them and they've likely evolved several times over in parallel evolution (or as the result of multiple infection and recombination maybe?)