`kubectl explain -o md`

**What would you like to be added**:
Markdown documentation export from a CRD using `kubectl explain -o md`
And ideally it would accept -i /path/to/local/crd.yaml

**Why is this needed**:
For auto generated documentation of an Custom Resource to markdown/html formats.

Start at the kubectl explain entry point and run the existing command against a CRD to understand its current output and resource lookup behavior. Trace how a CRD is loaded, including the proposed local crd.yaml path, and define the Markdown output shape. Done means explain supports -o md and, if included, -i for local CRDs with usable generated documentation.

Written by the indexing model from the issue text.