videoclip evaluation notebook/tutorial (facebookresearch#193)

Summary:
Add notebook tutorial for VideoCLIP evaluation using pretrained checkpoint.
- `retrieval/evaluation.ipynb`: notebook with step-by-step instructions for setting up model, calling model, and getting predictions

Pull Request resolved: facebookresearch#193

Test Plan:
Run notebook

Note that vscode is incapable of rendering video/audio in notebooks (see [issue](microsoft/vscode#118275)) and github doesn't display the videos in output cells. Embedded videos can be played in google colab ([link to this tutorial in colab](https://colab.research.google.com/drive/1zCU0KPzFKns07aVbSlN_1c8gtKXG0ke2?usp=sharing)) or in jupyter lab.

To install jupyterlab, convert your `torch-multimodal` conda env into a kernel, and launch jupyter lab:
```
(base) conda install -c conda-forge jupyterlab
(base) conda activate torch-multimodal
(torch-multimodal) conda install ipykernel
(torch-multimodal) ipython kernel install --user --name=torch-multimodal
(torch-multimodal) conda deactivate
(base) jupyter lab
```

Reviewed By: langong347

Differential Revision: D38362846

Pulled By: sophiazhi

fbshipit-source-id: aa18739cd02270ce80524d31cfd1a43b7e66287c