docs cgroups: add another example size for hugetlb

Add another example to clarify that HugePages smaller than 1MB will
be displayed using "KB", with an uppercased K (eg. 20KB), and not the
normal SI prefix kilo (small k).

Because of a misunderstanding/copy-paste error inside runc
(see https://github.com/opencontainers/runc/pull/2065), it tried
accessing the cgroup control file of a 64kB HugePage using
"hugetlb.64kB._____" instead of the correct "hugetlb.64KB._____".

Adding a new example will make it clear how sizes smaller than 1MB are
handled.
Signed-off-by: Odin Ugedal <odin@ugedal.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Documentation/cgroup-v1/hugetlb.txt

@@ -32,14 +32,18 @@ Brief summary of control files
  hugetlb.<hugepagesize>.usage_in_bytes     # show current usage for "hugepagesize" hugetlb
  hugetlb.<hugepagesize>.failcnt		   # show the number of allocation failure due to HugeTLB limit
 
-For a system supporting two hugepage size (16M and 16G) the control
+For a system supporting three hugepage sizes (64k, 32M and 1G), the control
 files include:
 
-hugetlb.16GB.limit_in_bytes
-hugetlb.16GB.max_usage_in_bytes
-hugetlb.16GB.usage_in_bytes
-hugetlb.16GB.failcnt
-hugetlb.16MB.limit_in_bytes
-hugetlb.16MB.max_usage_in_bytes
-hugetlb.16MB.usage_in_bytes
-hugetlb.16MB.failcnt
+hugetlb.1GB.limit_in_bytes
+hugetlb.1GB.max_usage_in_bytes
+hugetlb.1GB.usage_in_bytes
+hugetlb.1GB.failcnt
+hugetlb.64KB.limit_in_bytes
+hugetlb.64KB.max_usage_in_bytes
+hugetlb.64KB.usage_in_bytes
+hugetlb.64KB.failcnt
+hugetlb.32MB.limit_in_bytes
+hugetlb.32MB.max_usage_in_bytes
+hugetlb.32MB.usage_in_bytes
+hugetlb.32MB.failcnt