doc: Added new cache tiering doc to main docs.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Added new cache tiering doc to index/TOC.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Added cache tiering settings to ceph osd pool set.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Fix hyperlink to CRUSH maps.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
Merge pull request #1769 from ceph/wip-doc-cache-tier

doc: Support for cache tiering.