Update READMEs

s3-file-provider/README.md

@@ -1,3 +1,12 @@
 # S3 File Provider
 
-Example of using FileMiddleware to serve files stored on S3
+Example of using FileMiddleware to serve and cache files stored on S3.
+
+By providing a type conforming to `FileProvider` to `FileMiddleware` we can serve files from other sources than the local disk. This example creates two file providers, one that serves files from an S3 bucket and one that takes a base FileProvider and caches its results in memory. These two are combined to create a FileProvider that sources files from S3 and caches them in memory.
+
+The example needs two environment variables: 
+- `s3_file_region`: Defines the AWS region to use eg us-east-1
+- `s3_file_bucket`: The name of the bucket to serve files from
+
+There is an optional environment variable:
+- `s3_file_path`: Prefix to add when generating S3 file path.