update CONTRIBUTING.md for ccache (#41619)
Summary:
ccache now use cmake for building, update installation script.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41619
Reviewed By: zhangguanheng66
Differential Revision: D22644594
Pulled By: malfet
fbshipit-source-id: f894dd408822231f8aab36efbce188f06f004057
