docs: cgroup-v1: convert docs to ReST and rename to *.rst

Convert the cgroup-v1 files to ReST format, in order to
allow a later addition to the admin-guide.

The conversion is actually:
  - add blank lines and identation in order to identify paragraphs;
  - fix tables markups;
  - add some lists markups;
  - mark literal blocks;
  - adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup/cpuset.c

@@ -729,7 +729,7 @@ static inline int nr_cpusets(void)
  * load balancing domains (sched domains) as specified by that partial
  * partition.
  *
- * See "What is sched_load_balance" in Documentation/cgroup-v1/cpusets.txt
+ * See "What is sched_load_balance" in Documentation/cgroup-v1/cpusets.rst
  * for a background explanation of this.
  *
  * Does not return errors, on the theory that the callers of this