Supports of each DAMOS action and filters are up to DAMON operations set
implementation, but it's not mentioned in detail on the documentation. 
Update the information on the usage document.

Link: https://lkml.kernel.org/r/20230110190400.119388-5-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>