tools: bpftool: doc, fix incorrect text

Documentation about cgroup, feature, prog uses wrong header
'MAP COMMANDS' while listing commands. This patch corrects the header
in respective doc files.

Signed-off-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
Acked-by: Yonghong Song <yhs@fb.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/Documentation/bpftool-cgroup.rst

@@ -17,8 +17,8 @@ SYNOPSIS
 	*COMMANDS* :=
 	{ **show** | **list** | **tree** | **attach** | **detach** | **help** }
 
-MAP COMMANDS
-=============
+CGROUP COMMANDS
+===============
 
 |	**bpftool** **cgroup { show | list }** *CGROUP*
 |	**bpftool** **cgroup tree** [*CGROUP_ROOT*]