Pytorch example

[vishalbollu]

Closes #

https://colab.research.google.com/github/cortexlabs/cortex/blob/pytorch-imagenet/examples/image-classifier-pytorch/alexnet.ipynb

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Checklist:

• Run make test and make lint
• Test end to end manually (e.g. build/push all images, restart operator, and run cx refresh)
• Update examples
• Update documentation (add any new files to summary.md)
• Merge to master
• Cherry-pick into release branches if it's a bugfix
• Check gitbook that docs look good and links function properly
• Alert team if dev environment changed
• Delete the branch once it's merged

[deliahu]

This should be cortex-examples

[deliahu]

nit: new line at end of file