Update README.md

Added terminology

README.md

@@ -13,6 +13,19 @@ A web interface for [OpenDroneMap](https://github.com/OpenDroneMap/OpenDroneMap)
 - [ ] Documentation
 - [ ] Unit Testing
 
+## Terminology
+
+ - `Project`: A collection of tasks (successfully processed, failed, waiting to be executed, etc.)
+ - `Task`: A collection of input aerial images and an optional set of output results derived from the images, including an orthophoto, a georeferenced model and a textured model. A `Task`'s output is processed by OpenDroneMap.
+ - `ProcessingNode`: An instance usually running on a separate VM instance, or on a separate machine which accepts aerial images, runs OpenDroneMap and returns the processed results (orthophoto, georeferenced model, etc.). Each node communicates with WebODM via a lightweight API such as [node-OpenDroneMap](https://www.github.com/pierotofy/node-OpenDroneMap). WebODM manages the distribution of `Task` to different `ProcessingNode` instances.
+ - `ImageUpload`: aerial images.
+ - `Mission`: A flight path and other information (overlap %, angle, ...) associated with a particular `Task`.
+ 
+![image](https://cloud.githubusercontent.com/assets/1951843/17680196/9bfe878e-6304-11e6-852e-c09f1e02f3c0.png)
+
+![er diagram - webodm 2](https://cloud.githubusercontent.com/assets/1951843/17717379/4a227e28-63d3-11e6-9518-6a63cc1bcd3b.png)
+
+
 ## Work in progress
 
 We will add more information to this document soon (including information on how to get started).