Rename exercises dir

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

topics/aws/exercises/create_efs/exercise.md

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+## AWS - Create EFS
+ 
+### Requirements
+
+Two EC2 instances in different availability zones
+
+### Objectives
+
+1. Create an EFS with the following properties
+  1. Set lifecycle management to 60 days
+  2. The mode should match a use case of scaling to high levels of throughput and I/O operations per second
+2. Mount the EFS in both of your EC2 instances

topics/aws/exercises/create_efs/solution.md

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+## AWS - Create EFS
+ 
+### Requirements
+
+Two EC2 instances in different availability zones
+
+### Objectives
+
+1. Create an EFS with the following properties
+  1. Set lifecycle management to 60 days
+  2. The mode should match a use case of scaling to high levels of throughput and I/O operations per second
+2. Mount the EFS in both of your EC2 instances
+ 
+### Solution
+ 
+1. Go to EFS console
+2. Click on "Create file system"
+3. Create on "customize"
+  1. Set lifecycle management to "60 days since last access"
+  2. Set Performance mode to "MAX I/O" due to the requirement of "Scaling to high levels of throughput"
+  3. Click on "Next"
+  4. Choose security group to attach (if you don't have any, create one and make sure it has a rule to allow NFS traffic) and click on "Next" until you are able to review and create it
+5. SSH into your EC2 instances
+  1. Run `sudo yum install -y amazon-efs-utils`
+  2. Run `mkdir efs`
+  3. If you go to your EFS page and click on "Attach", you can see what ways are there to mount your EFS on your instancess
+    1. The command to mount the EFS should be similar to `sudo mount -t efs -o tls <EFS name>:/ efs` - copy and paste it in your ec2 instance's OS