Add the preferences documentation

Author: davetcc

content/arduino-libraries/io-abstraction/eeprom-impl-seamless-8-and-32-bit.md

@@ -83,6 +83,26 @@ Note that on the ESP range of devices, you'll need to call `EEPROM.begin(size)`
 
     ArduinoEEPROMAbstraction eepromWrapper(EEPROM);
 
+### EspPreferencesEeprom for ESP32 Preferences storage
+
+Requires ESP32 framework with Preferences library available for use. Note that in order to write back what's in memory you need to call `commit` to do the actual write.
+
+This class wraps the preferences API that's available on ESP32 Arduino framework. To use the wrapper first include:
+
+	#include <esp32/EspPreferencesEeprom.h>
+
+Then construct globally as follows:
+
+	EspPreferencesEeprom prefsStore(myNamespace, size);
+
+Where `myNamespace` is the namespace to use with preferences, and `size` is the size of the byte array it will create.
+
+Once you've finished writing values to it, flush the values out to storage as follows:
+
+    prefsStore.commit();
+
+A word of caution, do not call commit too often, this storage is probably in FLASH, and has limited write cycles.
+
 ### HalStm32EepromAbstraction for STM32 applications
 
 Requires version 1.8 of IoAbstraction.
@@ -166,4 +186,4 @@ Firstly, never call save in the menu item callback, *if using a rotary encoder t
 * Provide a save option somewhere that performs the save function.
 * Have a task manager event or task that listens for changes and saves a maximum of once every N minutes, where N is as large as you can tolerate. This may still write to EEPROM too frequently.
 
-[Go back to the IoAbstraction page]({{< relref "io-abstraction.md" >}})
+[Go back to the IoAbstraction page]({{< relref "io-abstraction.md" >}})