Update doc to reflect changes in issue: #3

[djmgit]

The doc needs to be update in order to add the changes done in issue #3

In short, the issue was about adding the capability to monitor changes in multiple ASGs for the
same backend.
For example, now for asg_name parameter we can define multiple ASGs separated by comma:
asg_name: asg1,asg2,asg3

However this feature is yet not mentioned in the doc.
The PR for this issue is this