doc: Improve the `awful` template client widget.

It was incorrectly sized.

tests/examples/awful/template.lua

@@ -156,12 +156,13 @@ local function client_widget(c, col, label)
             },
             layout = wibox.layout.stack
         },
-        border_width = bw,
-        border_color = bc,
-        shape_clip   = true,
-        fg           = beautiful.fg_normal or "#000000",
-        bg           = col,
-        shape        = function(cr2, w, h)
+        border_width    = bw,
+        border_color    = bc,
+        shape_clip      = true,
+        border_strategy = "inner",
+        fg              = beautiful.fg_normal or "#000000",
+        bg              = col,
+        shape           = function(cr2, w, h)
             return shape.rounded_rect(cr2, w, h, args.radius or 5)
         end,