Bug 1685177 - Update sccache-dist documentation for new config file path. r=mhentges

The config file location on macOS recently changed from `~/Library/Preferences/Mozilla.sccache/config`
to `~/Library/Application Support/Mozilla.sccache/config`, see https://github.com/mozilla/sccache/issues/919.

Differential Revision: https://phabricator.services.mozilla.com/D100822

build/docs/sccache-dist.rst

@@ -49,7 +49,7 @@ must read::
   ``~/.mozbuild/clang-dist-toolchain.tar.xz`` and
   ``~/.mozbuild/rustc-dist-toolchain.tar.xz``. This is an example of the paths
   that should be added to your client config to specify toolchains to build on
-  macOS, located at ``~/Library/Preferences/Mozilla.sccache/config``::
+  macOS, located at ``~/Library/Application Support/Mozilla.sccache/config``::
 
     [[dist.toolchains]]
     type = "path_override"