update README.md to reflect current build from source status on master (#92729)
Signed-off-by: Mike Brown <brownwm@us.ibm.com>
To avoid new contributor issues when building master a couple README.md comments will help... This change:
~~- Documents the current support restriction to apt package `g++-9` #91328 ** noting here that with the commit in https://github.com/pytorch/pytorch/pull/92911 g++-11.3 appears to build and run local tests at least as well as g++9, so this restriction may be overcome with that PR merge depending on success and CI updates.~~ (fixed now)
- Documents wip status for CUDA 12 #91122 (by forwarding to support matrix per suggestion)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/92729
Approved by: https://github.com/kit1980
