Jack cao g/r20 backportdoc (#4752)
* Update API GUIDE to include multi host training and add some colors (#4706)
* Update API GUIDE to include multi host training and add some colors
* address review comments
* Update README (#4734)
* Update README
* update user guide section title
* Add public readme for torchdynamo (#4744)
* Add public readme for torchdynamo
* Update index file
