Add/block mover component readme

[JustinyAhin]

Description

Added documentation for the block mover component (see #22891)

How has this been tested?

N/A, documentation only

Types of changes

Documentation

Checklist:

• [n/a] My code is tested.
• [n/a] My code follows the WordPress code style.
• [n/a] My code follows the accessibility standards.
• [n/a] My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR.

[JustinyAhin]

@youknowriad I was wondering where a contributor relatively new to some components (me 😀) can find docs about it.
For instance, for this particular one, I had to search through the code to find where some of the props are used; and guess what others do 😀.

[youknowriad]

These components in general are components that are not meant to be used by third-party developpers a lot, it's for advanced developpers that want to build their own editors. so right now, they are not really documented anywhere. In fact the work you're doing is the first attempt at this which is great.

[youknowriad]

I believe all the props aside clientIds are props provided by the interal withSelect which means you should remove them from the README.

[youknowriad]

Can we do the same as BlockBreadcrumb here (wrapping?)

[JustinyAhin]

Looks fine I think.

[youknowriad]

LGTM 👍