Improve backend documentation

[iaguis]

lokoctl backend documentation can use some improvements:

• We should give some hints to the user on how to create the resources needed to use the s3 backend, for example with the aws CLI tool:
  • create the S3 bucket for terraform

    aws s3 mb s3://jpetazzo-lokomotive-test --region=eu-central-1
    

  • create the DynamoDB db

    aws dynamodb create-table --table-name jpetazzo-lokomotive-test \
    --attribute-definitions AttributeName=LockID,AttributeType=S \
    --key-schema AttributeName=LockID,KeyType=HASH \
    --billing-mode=PAY_PER_REQUEST
    

• We should reference backend configuration on quickstarts

Reported-by: @jpetazzo

[iaguis]

This is included in the S3 configuration reference now.