Update README and CHANGELOG for v25 release (awslabs#89)

Scrub temporary build-time keypair

This keypair is an artifact of the build process- it's a temporary key and does not represent a secrity risk. However, it is a best practice to remove these keys before publishing, so we've added a step to remove it for all future AMI

Add ability to modify node root volume size

* Add ability modify root volume size

Added updated binaries

* added renamed aws-iam-authenticator binary
* check sha256sum on binary download
* added nfs-utils for EFS support
* add source_ami_filter to packer script

Added updated binaries

* added renamed aws-iam-authenticator binary
* check sha256sum on binary download
* added nfs-utils for EFS support
* add source_ami_filter to packer script

Initial release