docs/scheduler/sched-bwc: note/link cgroup v2

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20210120001824.385168-6-kolyshkin@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/cgroup-v2.rst

+.. _cgroup-v2:
+
 ================
 Control Group v2
 ================
@@ -954,6 +956,8 @@ All cgroup core files are prefixed with "cgroup."
 Controllers
 ===========
 
+.. _cgroup-v2-cpu:
+
 CPU
 ---
 

Documentation/scheduler/sched-bwc.rst

@@ -26,6 +26,11 @@ Management
 ----------
 Quota and period are managed within the cpu subsystem via cgroupfs.
 
+.. note::
+   The cgroupfs files described in this section are only applicable
+   to cgroup v1. For cgroup v2, see
+   :ref:`Documentation/admin-guide/cgroupv2.rst <cgroup-v2-cpu>`.
+
 - cpu.cfs_quota_us: the total available run-time within a period (in
   microseconds)
 - cpu.cfs_period_us: the length of a period (in microseconds)