Write README for terraform

Author: mrkn

terraform/README.md

@@ -0,0 +1,35 @@
+# Prepare envchain
+
+To manage credentials of AWS account, it is recommended to use [envchain](https://github.com/sorah/envchain).
+
+```
+$ envchain -s aws-ruby-data-discourse AWS_ACCESS_KEY_ID AWS_SECRET_ACCESS_KEY
+aws-ruby-data-discourse.AWS_ACCESS_KEY_ID: <input access key>
+aws-ruby-data-discourse.AWS_SECRET_ACCESS_KEY: <input secret>
+```
+
+# Prepare terraform
+
+```
+$ envchain aws-ruby-data-discourse terraform init
+```
+
+# Select workspace
+
+We have two workspaces: (1) `test`, and (2) `prod`. `test` workspace is for testing, and `prod` workspace is for production.
+
+```
+$ envchain aws-ruby-data-discourse terraform workspace show
+
+$ envchain aws-ruby-data-discourse terraform workspace select test
+
+$ envchain aws-ruby-data-discourse terraform workspace select prod
+```
+
+# Execute terraform
+
+```
+$ envchain aws-ruby-data-discourse terraform plan
+
+$ envchain aws-ruby-data-discourse terraform apply
+```