[MultiKueue] Document how to use training-operator with managedBy

[mimowo]

What would you like to be added:

Document how to use managedBy provided by the training-operator.

It will be based on a dev (master) version of the training-operator until the official release.

Why is this needed:

To show users how to use the training-operator with MultiKueue.

Completion requirements:

This enhancement requires the following artifacts:

• Docs update

The artifacts should be linked in subsequent comments.

[mimowo]

/assign @mszadkow
/cc @trasc @mwielgus @tenzen-y