Updates readme documentation

Author: ndorin

README.md

@@ -8,6 +8,15 @@ Provided under MIT license
 
 Fork this repo when creating a new plugin for Essentials. For more information about plugins, refer to the Essentials Wiki [Plugins](https://github.com/PepperDash/Essentials/wiki/Plugins) article.
 
+This repo contains example classes for the three main categories of devices:
+* `EssentialsPluginTemplateDevice`: Used for most third party devices which require communication over a streaming mechanism such as a Com port, TCP/SSh/UDP socket, CEC, etc
+* `EssentialsPluginTemplateLogicDevice`:  Used for devices that contain logic, but don't require any communication with third parties outside the program
+* `EssentialsPluginTemplateCrestronDevice`:  Used for devices that represent a piece of Crestron hardware
+
+There are matching factory classes for each of the three categories of devices.  The `EssentialsPluginTemplateConfigObject` should be used as a template and modified for any of the categories of device.  Same goes for the `EssentialsPluginTemplateBridgeJoinMap`.
+
+This also illustrates how a plugin can contain multiple devices.
+
 ## Cloning Instructions
 
 After forking this repository into your own GitHub space, you can create a new repository using this one as the template.  Then you must install the necessary dependencies as indicated below.