README.md in terraforming-0.15.0 vs README.md in terraforming-0.16.0

@@ -23,11 +23,13 @@
 - [Contributing](#contributing)
 - [License](#license)
 
 ## Supported version
 
-Ruby 2.1 or higher
+- Ruby 2.1 or higher is required
+- Terraform v0.9.3 or higher is recommended
+  - Some resources (e.g. `iam_instance_profile`) uses newer resource specification
 
 ## Installation
 
 Add this line to your application's Gemfile:
 
@@ -61,9 +63,15 @@
 aws_access_key_id = Hoge
 aws_secret_access_key = FugaFuga
 
 # Pass profile name by --profile option
 $ terraforming s3 --profile hoge
+```
+
+You can assume a role by using the `--assume` option.
+
+```bash
+$ terraforming s3 --assume arn:aws:iam::123456789123:role/test-role
 ```
 
 You can force the AWS SDK to utilize the CA certificate that is bundled with the SDK for systems where the default OpenSSL certificate is not installed (e.g. Windows) by utilizing the `--use-bundled-cert` option.
 
 ```bash