updated readme (#22)

Signed-off-by: Mark <[email protected]>

README.md

@@ -1,5 +1,19 @@
 # docker-prometheus
+This repository contains code to create an image that runs Prometheus to be used within AWS.
+A version of Prometheus is downloaded based on the PROMETHEUS_VERSION arg within the Dockerfile. Prometheus configuration files are then
+fetched from S3 and Prometheus is started.
+
+
+# Required Environment Variables
+
+|             Key            |                                Description               |
+|----------------------------|----------------------------------------------------------|
+| PROMETHEUS_CONFIG_S3_BUCKET   | The ID of the config S3 bucket                           |
+| PROMETHEUS_CONFIG_S3_PREFIX   | The directory path of the config files within the bucket |
+| AWS_ACCESS_KEY_ID          | AWS access key                           |
+| AWS_SECRET_ACCESS_KEY      | AWS secret access key |
+
+
+
 
-# Description
-Repo for the DataWorks Prometheus Docker image