doc: Add the markup example of popup_calendar

Refer to tests/examples/awful/widget/calendar_popup/default.lua

lib/awful/widget/calendar_popup.lua

@@ -46,6 +46,9 @@ local styles = { "year", "month", "yearheader", "monthheader", "header", "weekda
 -- @tparam cell_properties table Table of cell style properties
 
 --- Cell properties.
+--
+-- @DOC_awful_widget_calendar_popup_cell_properties_EXAMPLE@
+--
 -- @field markup Markup function or format string
 -- @field fg_color Text foreground color
 -- @field bg_color Text background color

tests/examples/awful/widget/calendar_popup/cell_properties.lua

@@ -0,0 +1,42 @@
+--DOC_HIDE_START --DOC_GEN_IMAGE
+local awful = require("awful")
+local wibox = require("wibox")
+
+screen[1]._resize { width = 480, height = 200 }
+
+local wb = awful.wibar { position = "top", }
+
+-- Create the same number of tags as the default config
+awful.tag({ "1", "2", "3", "4", "5", "6", "7", "8", "9" }, screen[1], awful.layout.layouts[1])
+
+-- Only bother with widgets that are visible by default
+local mykeyboardlayout = awful.widget.keyboardlayout()
+local my_text_clock = wibox.widget.textclock()
+local mytaglist = awful.widget.taglist(screen[1], awful.widget.taglist.filter.all, {})
+local mytasklist = awful.widget.tasklist(screen[1], awful.widget.tasklist.filter.currenttags, {})
+--DOC_HIDE_END
+
+local my_header_properties = {
+    markup = function(text) return "<i>" .. text .. "</i>" end,
+}
+local my_options = { style_header = my_header_properties, }
+local month_calendar = awful.widget.calendar_popup.month(my_options)
+month_calendar:attach(my_text_clock, "tr")
+
+--DOC_HIDE_START
+wb:setup {
+    layout = wibox.layout.align.horizontal,
+    {
+        mytaglist,
+        layout = wibox.layout.fixed.horizontal,
+    },
+    mytasklist,
+    {
+        layout = wibox.layout.fixed.horizontal,
+        mykeyboardlayout,
+        my_text_clock,
+    },
+}
+month_calendar:toggle()
+
+--vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80 --DOC_HIDE_END