~/.config/dwm: Add shortcut for music player

.config/dwm/config.h

	{ "Gimp",     NULL,       NULL,       0,            1,           -1 },
	//{ "Firefox",  NULL,       NULL,       1 << 8,       0,           -1 },
	{ "Quodlibet", NULL,      NULL,       1 << 4,       0,           -1 },
	// float pinboard/popup windows
	//{ "Firefox",  NULL,       "",       0,       1,           -1 },
};
static const char *volumedowncmd[] = { "amixer", "set", "Master", "5%-", NULL };
static const char *volumeupcmd[] = { "amixer", "set", "Master", "5%+", NULL };
static const char *volumetogglecmd[] = { "amixer", "set", "Master", "toggle", NULL };
static const char *musicplayercmd[] = { "quodlibet", NULL };
static const char *screenlockcmd[] = { "slock", NULL };
	{ 0,                            XF86XK_AudioRaiseVolume, spawn, { .v = volumeupcmd } },
	{ 0,                            XF86XK_AudioMute       , spawn, { .v = volumetogglecmd } },
	{ MODKEY|ShiftMask,             XK_m,                    view,  {.ui = 1 << 4} },
	{ MODKEY|ShiftMask,             XK_m,                    spawn, { .v = musicplayercmd } },
	{ MODKEY|ShiftMask,             XK_l,      spawn,          { .v = screenlockcmd } },
};