docs: cgroup-v1: use numbered lists for user interface setup

Setup instructions for memory resource controller UI uses a mix of
section headings and normal paragraphs, whereas numbered lists are
better fit for this purpose.

While at it, also slightly reword the instructions and add reference to
"Why are cgroups needed?" in the main cgroups documentation.

Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Author: bagasme

Documentation/admin-guide/cgroup-v1/cgroups.rst

@@ -80,6 +80,8 @@ access. For example, cpusets (see Documentation/admin-guide/cgroup-v1/cpusets.rs
 you to associate a set of CPUs and a set of memory nodes with the
 tasks in each cgroup.
 
+.. _cgroups-why-needed:
+
 1.2 Why are cgroups needed ?
 ----------------------------
 

Documentation/admin-guide/cgroup-v1/memory.rst

@@ -387,30 +387,30 @@ U != 0, K >= U:
 3. User Interface
 =================
 
-3.0. Configuration
-------------------
-
-a. Enable CONFIG_CGROUPS
-b. Enable CONFIG_MEMCG
-
-3.1. Prepare the cgroups (see cgroups.txt, Why are cgroups needed?)
--------------------------------------------------------------------
+To use the user interface:
 
-::
+1. Enable CONFIG_CGROUPS and CONFIG_MEMCG options
+2. Prepare the cgroups (see :ref:`Why are cgroups needed?
+   <cgroups-why-needed>` for the background information)::
 
 	# mount -t tmpfs none /sys/fs/cgroup
 	# mkdir /sys/fs/cgroup/memory
 	# mount -t cgroup none /sys/fs/cgroup/memory -o memory
 
-3.2. Make the new group and move bash into it::
+3. Make the new group and move bash into it::
 
 	# mkdir /sys/fs/cgroup/memory/0
 	# echo $$ > /sys/fs/cgroup/memory/0/tasks
 
-Since now we're in the 0 cgroup, we can alter the memory limit::
+4. Since now we're in the 0 cgroup, we can alter the memory limit::
 
 	# echo 4M > /sys/fs/cgroup/memory/0/memory.limit_in_bytes
 
+   The limit can now be queried::
+
+	# cat /sys/fs/cgroup/memory/0/memory.limit_in_bytes
+	4194304
+
 .. note::
    We can use a suffix (k, K, m, M, g or G) to indicate values in kilo,
    mega or gigabytes. (Here, Kilo, Mega, Giga are Kibibytes, Mebibytes,
@@ -422,10 +422,6 @@ Since now we're in the 0 cgroup, we can alter the memory limit::
 .. note::
    We cannot set limits on the root cgroup any more.
 
-::
-
-  # cat /sys/fs/cgroup/memory/0/memory.limit_in_bytes
-  4194304
 
 We can check the usage::