Auto grad accum example (#742)
* Auto grad accum example
* Include auto grad accum to exlcusion list
* Typo fix calculate -> calculate
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
