Correct command syntax for blackbox/fluxbox

Replace the parentheses with braces for the menu updating commands in
the blackbox and fluxbox sections.

README.md

@@ -31,7 +31,7 @@ submenu. For example, add this somewhere in your `~/.blackbox/menu` file:
 You can add the xdgmenumaker command as another item in your menu, if
 you want to update it, without having to run the command manually again:
 
-    [exec] (Update Blackbox Menu) (xdgmenumaker -f blackbox > ~/.blackbox/xdg_menu)
+    [exec] (Update Blackbox Menu) {xdgmenumaker -f blackbox > ~/.blackbox/xdg_menu}
 
 
 Fluxbox
@@ -49,7 +49,7 @@ submenu. For example, add this somewhere in your `~/.fluxbox/menu` file:
 You can add the xdgmenumaker command as another item in your menu, if
 you want to update it, without having to run the command manually again:
 
-    [exec] (Update Fluxbox Menu) (xdgmenumaker -f fluxbox > ~/.fluxbox/xdg_menu)
+    [exec] (Update Fluxbox Menu) {xdgmenumaker -f fluxbox > ~/.fluxbox/xdg_menu}
 
 
 IceWM

man/xdgmenumaker.t2t

@@ -104,7 +104,7 @@ You can add the **xdgmenumaker** command as another item in your menu,
 if you want to update it, without having to run the command manually
 again:
 
-``[exec] (Update Blackbox Menu) (xdgmenumaker -f blackbox > ~/.blackbox/xdg_menu)``
+``[exec] (Update Blackbox Menu) {xdgmenumaker -f blackbox > ~/.blackbox/xdg_menu}``
 
 
 : **Fluxbox**
@@ -123,7 +123,7 @@ You can add the **xdgmenumaker** command as another item in your menu,
 if you want to update it, without having to run the command manually
 again:
 
-``[exec] (Update Fluxbox Menu) (xdgmenumaker -f fluxbox > ~/.fluxbox/xdg_menu)``
+``[exec] (Update Fluxbox Menu) {xdgmenumaker -f fluxbox > ~/.fluxbox/xdg_menu}``
 
 
 : **IceWM**