https://github.com/rook/rook/pull/11845 added dynamic label `mgr_role`.
The example yaml files are updated but this doc is missed.
I think it would be better to refer to `deploy/examples` but I find all
other places are not doing that. So keep it inlined to be consistent.
Signed-off-by: Bin Wang <bin.wang@mail.binwang.me>
(cherry picked from commit 25d89d2b68)