Add instructions for custom formatted time sensor (#15086)

source/_integrations/time_date.markdown

@@ -31,6 +31,33 @@ sensor:
 
 - **display_options** array (*Required*): The option to display. The types *date_time*, *date_time_utc*, *time_date*, and *date_time_iso* shows the date and the time. The other types just the time or the date. *beat* shows the [Swatch Internet Time](https://www.swatch.com/en_us/internet-time).
 
+Sensors including the time update every minute, the date sensor updates each day at midnight, and the beat sensor updates with each beat (86.4 seconds).
+
 <p class='img'>
   <img src='/images/screenshots/time_date.png' />
 </p>
+
+# Producing your own custom time and date sensor
+
+Whilst there are a number of `display_options` exposed by this sensor, they cannot hope to satisfy everyone, and large parts of the world will find that their local display conventions are not included.
+
+The following can be used to create a time and date sensor whose output can be properly customised to use your own preferred formatting, specified in the call to timestamp_custom() using standard [Python datetime formatting](https://docs.python.org/3.8/library/datetime.html#strftime-and-strptime-behavior).
+
+{% raw %}
+
+```yaml
+sensor:
+  # Minimal configuration of the standard time and date sensor
+  - platform: time_date
+    display_options:
+      - 'date_time_iso'
+  # Build on the standard sensor to produce one that can be customized    
+  - platform: template
+    sensors:
+      time_formatted:
+        friendly_name: "Date and time"
+        value_template: "{{ as_timestamp(states('sensor.date_time_iso')) | timestamp_custom('%A %B %-m, %I:%M %p') }}"
+        icon_template: mdi:calendar-clock
+```        
+
+{% endraw %}