Rename exercises dir

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

topics/aws/exercises/auto_scaling_groups_basics/exercise.md

@@ -0,0 +1,21 @@
+## AWS Auto Scaling Groups - Basics
+
+### Requirements
+
+Zero EC2 instances running
+
+### Objectives
+
+A. Create a scaling group for web servers with the following properties:
+  * Amazon Linux 2 AMI
+  * t2.micro as the instance type
+  * user data:
+```
+yum install -y httpd
+systemctl start httpd
+systemctl enable httpd
+```
+
+B. Were new instances created since you created the auto scaling group? How many? Why?
+C. Change desired capacity to 2. Did it launch more instances?
+D. Change back the desired capacity to 1. What is the result of this action?