[Docs] Add Mention of Plural Units in Docs's Table for Better Visibility

[custardcream98]

I didn't realize there was no difference between using plural units or singular ones. It might seem obvious, but as a non-native English speaker, it was difficult for me to know until I actually looked at the day.js code. I thought it would be helpful to clarify in the docs that plural units are also valid and treated the same.

I wanted to contribute this suggestion, but it seems the day.js.org is not maintained in this repo, so I’m posting an issue here instead.

I saw there’s a mention of plural units here, but could you please also add this information to the table below for better clarity?

While I admit this confusion came from not reading the documentation thoroughly, I still believe adding this to the table would make it even clearer for users.

Thank you for your time and for considering this suggestion!