tools: bpftool: doc, add text about feature-subcommand

This patch adds missing information about feature-subcommand in
bpftool.rst

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

tools/bpf/bpftool/Documentation/bpftool.rst

@@ -16,7 +16,7 @@ SYNOPSIS
 
 	**bpftool** **version**
 
-	*OBJECT* := { **map** | **program** | **cgroup** | **perf** | **net** }
+	*OBJECT* := { **map** | **program** | **cgroup** | **perf** | **net** | **feature** }
 
 	*OPTIONS* := { { **-V** | **--version** } | { **-h** | **--help** }
 	| { **-j** | **--json** } [{ **-p** | **--pretty** }] }
@@ -34,6 +34,8 @@ SYNOPSIS
 
 	*NET-COMMANDS* := { **show** | **list** | **help** }
 
+	*FEATURE-COMMANDS* := { **probe** | **help** }
+
 DESCRIPTION
 ===========
 	*bpftool* allows for inspection and simple modification of BPF objects