update readme with more info

README.md

@@ -2,6 +2,15 @@
 
 This utility interacts with the Fairwinds BIF-Server to find base images and report on their vulnerabilities.
 
+## What and Why is it?
+
+When using a container scanning tool to identivy known vulnerabilities (CVEs, or common vulnerabilities and exposures), it can be difficult to understand _where_ the vulnerabilities exist in the container, and how to mitigate them. Often, the simplest and most efficient mitigation is to update the "base image" - or the image used in the `FROM` statement in your container definition.
+
+BIF allows you to understand the impact of updating the base image of your container will have.
+  * First, it can detect what base image the container is using, even though it doesn't have access to the Dockerfile.
+  * Second, it will show you what vulnerabilities are present in that base image.
+  * Lastly, it will show you what versions of that base image don't have that vulnerability.
+
 ## Installation
 
 Download the latest binary from: https://github.com/FairwindsOps/bif/releases