kubernetes/community repo's commit 3034683c5997474d9f59ef722c8ee9c1f1e58f07
started a re-org of the design-proposals directory to have hierarchical
structure and subdirectories.  This in turn broke the urls in the
kubernetes/kubernetes/pkg/cloud-provider/README.md file.  This patch adds
the appropriate subdirectories into the urls in the readme.

While the kubernetes/kubernetes/pkg/cloud-provider/cloud-provider
directory represents an area that's deprecated now, this patch isn't
introducing anything new, but rather fixes the broken links to
information on the deprecation and info on the evolving forward
path for the cloud providers.
Signed-off-by: Tim Pepper <tpepper@vmware.com>