Rename exercises dir

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

topics/aws/exercises/budget_setup/exercise.md

@@ -0,0 +1,5 @@
+## AWS - Budget Setup
+
+### Objectives
+
+Setup a cost budget in your AWS account based on your needs.

topics/aws/exercises/budget_setup/solution.md

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+## AWS - Budget Setup
+
+### Objectives
+
+Setup a cost budget in your AWS account based on your needs.
+
+### Solution
+
+1. Go to "Billing"
+2. Click on "Budgets" in the menu
+3. Click on "Create a budget"
+4. Choose "Cost Budget" and click on "Next"
+5. Choose the values that work for you. For example, recurring monthly budget with a specific amount
+6. Insert a budget name and Click on "Next" 
+7. Set up an alert but clicking on "Add an alert threshold"
+  1. Set a threshold (e.g. 75% of budgeted amount)
+  2. Set an email where a notification will be sent
+8. Click on "Next" until you can click on "Create a budget"