sched_deadline, docs: fix cpuset example for cgroupv2

sched_deadline, docs: fix cpuset example for cgroupv2

Documenation/scheduler/sched-deadline.rst provides two examples for how
to setup cgroup and cpuset for deadline tasks: one for cgroup v1 and one
cgroup v2. The code block in the latter is not properly html rendered as
the :: marker is missing.

Add the :: marker before the code block for the cgroup v2 example to fix
html rendering.

Also make the example description more explicit for better clarity.

Fixes: 0116765035eb ("sched_deadline, docs: add affinity setting with cgroup2 cpuset controller")
Signed-off-by: Matteo Martelli <matteo.martelli@codethink.co.uk>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20260223-docs-sched-deadline-fix-example-v1-1-8d0bedc2bc6f@codethink.co.uk>