Add motivation section to README

README.md

@@ -3,6 +3,16 @@
 # Prombox
 Sandbox environment for editing and testing prometheus configuration on the fly.
 
+## Motivation
+
+[Prometheus](https://prometheus.io) users often have trouble configuring new targets or creating alerts and recording rules because getting the YAML syntax exactly right can be a struggle. When running Prometheus locally this isn't as big of a challenge because you have direct access to the config file and can make changes quickly. Once Prometheus is deployed into a production environment, however, this becomes challenging because you don't have the ability to re-create the same combination of configuration and environment.
+
+This is especially challenging when you're taking advange of some service discovery methods provided by Prometheus, like AWS EC2 discovery. You may be able to discover your instance hosts via the AWS EC2 API, but accessing the endpoint your application exposes metrics on may not work due to firewall rules. Prometheus needs to live within your AWS VPC or private network in order for the metric scraping to occur successfully.
+
+For these reasons, we built "Prombox", a lightweight UI that allows users to build the Prometheus config file and alerts/recording rules. This could be deployed within your environment (AWS VPC, etc) along with an instance of Prometheus that mimics your production instance. This would create a "sandbox" that allows you to "play" with new rules and configuration options to see how they would work.
+
+![](docs/images/prombox.png)
+
 ## Build and Run Docker image
 
 ### Build Prombox