crush: add note about r in recursive choose
crush: add note about r in recursive choose

Reflects ceph.git commit 4551fee9ad89d0427ed865d766d0d44004d3e3e1.

Signed-off-by: Ilya Dryomov <33f1a10eef0a3354755a1541edfdb100ff87fcfc@inktank.com>
Reviewed-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@inktank.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs