quant docs: best practices for quantization accuracy debugging
Summary:
This PR creates a best practices guideline for debugging quantization
accuracy. The content here comes from https://fburl.com/gdoc/nzlzxeaf,
with experimental and Meta-only parts left out.
For now, a lot of the debugging is manual, with the Numeric Suite the
only tool we have to help the user find root causes of quantization
inaccuracies. As we build additional tools for equalization detection,
outlier detection, etc, we will add them to this page
Test plan:
```
cd docs
make html
cd build/html
python -m server.http
// result renders well in browser
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/77536
Approved by: https://github.com/hx89
