[Doc] Missing Artifact in Doc Guide

In our doc guide for [MLModel -> Updatable Models -> Pipeline Classifier](https://apple.github.io/coremltools/docs-guides/source/updatable-tiny-drawing-classifier-pipeline-model.html#get-the-embedding-model), we mentioned an artifact `./models/TinyDrawingEmbedding.mlmodel`
```
import coremltools
from coremltools.models import MLModel

embedding_path = './models/TinyDrawingEmbedding.mlmodel'
embedding_model = MLModel(embedding_path)

embedding_spec = embedding_model.get_spec()
print embedding_spec.description
```
However, we didn't mention where to obtain `./models/TinyDrawingEmbedding.mlmodel`

Open the linked Updatable Models guide and locate the section containing the `TinyDrawingEmbedding.mlmodel` example and its `MLModel` loading snippet. Trace the referenced `./models/TinyDrawingEmbedding.mlmodel` artifact from the guide context, then document where readers can obtain it; the guide should no longer reference the artifact without an acquisition path.

Written by the indexing model from the issue text.