ccache README recommendation
only allow one cache at a time

This will prevent the ~/.kpatch cache directory from filling up with old
caches.
Merge pull request #27 from jpoimboe/readme-ccache

ccache README recommendation
Merge pull request #28 from jpoimboe/clean-cache

only allow one cache at a time
iterate the iterator

It works better this way.  Trust me.

Signed-off-by: Seth Jennings <sjenning@redhat.com>
Merge pull request #29 from spartacus06/fixes

iterate the iterator
add warnings, limitations, mailing list to README
Merge pull request #30 from jpoimboe/readme-caveats

add warnings, limitations, mailing list to README