Update documentation for the new config file path on macOS.
Update documentation for the new config file path on macOS.

Fixes #919.

This path changed due to the update of the directories dependency
in commit 185c6ba4b0d360e6be8daf15a9fb80899c030df5.

luser/sccache2,mozilla/sccache,luser/sccache2,luser/sccache2,mozilla/sccache,luser/sccache2,mozilla/sccache