Fix paths in the comments for core-docs target.

A couple of the paths describing where the output of this target
appears appear to have changed at some point. This comment updates the
comments that describe the behaviour accordingly.

Test: `make core-docs` and verify that the files appear at the given paths
Change-Id: I6d63960bf2bfb4b4cd20ef9d185c90a29f4f7ebc