doc(w.c.radialprogressbar): Show example code

Adds the code snippet for the example shown in the module description.

Signed-off-by: Lucas Schwiderski <lucas@lschwiderski.de>

tests/examples/wibox/container/defaults/radialprogressbar.lua

@@ -1,4 +1,4 @@
---DOC_HIDE_ALL
+--DOC_HIDE_START
 --DOC_GEN_IMAGE
 local wibox = require("wibox")
 
@@ -9,6 +9,7 @@ return {
     widget = wibox.widget.textbox,
 },
 {
+--DOC_HIDE_END
     {
         {
             text   = "After",
@@ -21,8 +22,9 @@ return {
         min_value = 0,
         widget    = wibox.container.radialprogressbar
     },
+--DOC_HIDE_START
     margins = 5,
     layout = wibox.container.margin
 }
 
---DOC_HIDE vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80
+-- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80