Make S3 into a link, for consistency.

README.md

@@ -4,7 +4,7 @@ Docker image for performing simple backups of Docker volumes. Main features:
 
 - Mount volumes into the container, and they'll get backed up
 - Use full `cron` expressions for scheduling the backups
-- Backs up to local disk, AWS S3, or both
+- Backs up to local disk, [AWS S3](https://aws.amazon.com/s3/), or both
 - Optionally stops other containers for the duration of the backup, and starts them again afterward, to ensure consistent backups of things like database files, etc
 
 ## Examples