add readme and notice at the top of config.yml (#17323)
Summary:
reorder some envars for consistency
add readme and notice at the top of config.yml
generate more yaml from Python
closes #17322
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17323
Differential Revision: D14186734
Pulled By: kostmo
fbshipit-source-id: 23b2b2c1960df6f387f1730c8df1ec24a30433fd
