Rename exercises dir

Name it instead "topics" so it won't be
strange if some topics included "exercises" directory.

topics/terraform/exercises/s3_bucket_rename/exercise.md

@@ -0,0 +1,20 @@
+# Rename S3 Bucket
+
+## Requirements
+
+* An existing S3 bucket tracked by Terraform.
+If you don't have it, you can use the following block and run `terraform apply`:
+
+```terraform
+resource "aws_s3_bucket" "some_bucket" {
+    bucket = "some-old-bucket"
+}
+```
+
+## Objectives
+
+1. Rename an existing S3 bucket and make sure it's still tracked by Terraform
+
+## Solution
+
+Click [here to view the solution](solution.md)