Document asymmetric matching capabilities

## 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:

```js
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

Locate the library's matcher documentation and the section covering toBeArrayOf and expect.toBeDateInMonth. Document asymmetric matching using the example in the issue, and note Vitest compatibility; done when both points are discoverable in the documentation.

Written by the indexing model from the issue text.