Clarify that the amazonlinux container image is minimal

Resolves aws/amazon-linux-docker-images#10.

amazonlinux/content.md

@@ -1,6 +1,8 @@
 ## What is Amazon Linux?
 
-Amazon Linux is provided by Amazon Web Services (AWS). It is designed to provide a stable, secure, and high-performance execution environment for applications running on Amazon EC2. It also includes packages that enable easy integration with AWS, including launch configuration tools and many popular AWS libraries and tools. AWS provides ongoing security and maintenance updates to all instances running Amazon Linux.
+Amazon Linux is provided by Amazon Web Services (AWS). It is designed to provide a stable, secure, and high-performance execution environment for applications running on Amazon EC2. The full distribution includes packages that enable easy integration with AWS, including launch configuration tools and many popular AWS libraries and tools. AWS provides ongoing security and maintenance updates to all instances running Amazon Linux.
+
+The Amazon Linux container image contains a minimal set of packages. To install additional packages, [use `yum`](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/managing-software.html).
 
 AWS provides two versions of Amazon Linux: [Amazon Linux 2](https://aws.amazon.com/amazon-linux-2/) LTS Candidate and [Amazon Linux AMI](https://aws.amazon.com/amazon-linux-ami/).