docs: Provide instructions for s3 backend prerequisites

Related to #226

docs/configuration-reference/backend/s3.md

@@ -19,8 +19,23 @@ used.
 
 ## Prerequisites
 
-* AWS S3 bucket to be used should already be created.
+* AWS S3 bucket to be used should already be created. You can do this by running the following AWS CLI command:
+
+```sh
+aws s3 mb s3://kinvolk-lokomotive-test --region=eu-central-1
+```
+
 * DynamoDB table to be used for state locking should already be created. The table must have a primary key named LockID.
+You can create it with the following AWS CLI command:
+
+
+```sh
+aws dynamodb create-table --table-name kinvolk-lokomotive-test \
+--attribute-definitions AttributeName=LockID,AttributeType=S \
+--key-schema AttributeName=LockID,KeyType=HASH \
+--billing-mode=PAY_PER_REQUEST
+```
+
 * The necessary [IAM permissions](#iam-permissions) for S3 and DynamoDB.
 
 ## Configuration