Adds carbon intensity graph example.

micropython/examples/gfx_pack/README.md

@@ -12,6 +12,7 @@
   - [CO2](#co2)
   - [Thermometer](#thermometer)
 - [Wireless Examples](#wireless-examples)
+  - [Carbon Intensity Graph](#carbon-intensity-graph)
   - [Sunrise / Sunset](#sunrise--sunset)
   - [Zoo Facts](#zoo-facts)
 - [Other Resources](#other-resources)
@@ -104,6 +105,14 @@ These wireless examples need `network_manager.py` and `WIFI_CONFIG.py` from the
 
 - [micropython/examples/common](../../examples/common)
 
+### Carbon Intensity Graph
+
+[carbon_intensity.py](carbon_intensity.py)
+
+Displays near realtime information about the different types of electricity generation for a given UK postcode area.  Uses the backlight and a bar graph to show the current mix of generation sources, and updates itself periodically or when button E is pressed.
+
+Find out more about the Carbon Intensity API here:  https://carbon-intensity.github.io/api-definitions/#carbon-intensity-api-v2-0-0
+
 ### Sunrise / Sunset
 
 [sunrise.py](sunrise.py)