Add training paper to README.md

[codyaustun]

I am following up on Christine Cheng's suggestion to add the papers to the GitHub repositories.

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[codyaustun]

@googlebot I signed it!

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CLAs look good, thanks!

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[codyaustun]

@TheKanter @petermattson I just remembered I created a PR for this a while ago.

[TheKanter]

@codyaustun I manually inserted these changes b/c I cannot figure out how to remove the conflict. Can you review the new readme and make sure I did it correctly? If so, please close :)

[codyaustun]

Looks good to me.