docs: Replace create with new

[NiwakaDev]

Before this commit, I got the following error:

no function or associated item named `create` found for struct `opendal::Operator` in the current scope
function or associated item not found in `Operator`

So, I replaced the create method with the new method.

[Xuanwo]

Thanks a lot!

[Xuanwo]

You are the 100th contributor of OpenDAL. Congrats! Happy to have you here!