Document asymmetric matching capabilities

[emahuni]

Description

This library is very good. However the documentation doesn't mention that the matchers are also asymmetric. I had to test this by doing:

expect([{ dt: new Date('2021-08-29') }]).toBeArrayOf({ dt: 
   expect.toBeDateInMonth(7)
 });

It'd be nice if this was mentioned as this is one of the best things about this lib.

Also document that this works with Vitest

[JamieMason]

Thanks @emahuni, this is a good idea. Keep an eye on #51 though as some of the non-trivial matchers have some issues when used as asymmetric matchers at the moment