doc: Add 'server' command in help

'server' is the last common command which is not in CLI help.
IMHO, adding this small documentation could help to promote usage of
pkcs11 forwarding.

p11-kit/p11-kit.c

@@ -63,6 +63,7 @@ int       p11_kit_external        (int argc,
 static const p11_tool_command commands[] = {
 	{ "list-modules", p11_kit_list_modules, "List modules and tokens" },
 	{ "remote", p11_kit_external, "Run a specific PKCS#11 module remotely" },
+	{ "server", p11_kit_external, "Run a server process that exposes PKCS#11 module remotely" },
 	{ P11_TOOL_FALLBACK, p11_kit_external, NULL },
 	{ 0, }
 };