Fix AS::Notification.subscribe arguments in README.md

[tisba]

ActiveSupport::Notifications.subscribe's block arguments are as follows (taken from the Rails API docs):

ActiveSupport::Notifications.subscribe('render') do |name, start, finish, id, payload|
  name    # => String, name of the event (such as 'render' from above)
  start   # => Time, when the instrumented block started execution
  finish  # => Time, when the instrumented block ended execution
  id      # => String, unique ID for the instrumenter that fired the event
  payload # => Hash, the payload
end

The README makes it look like the id argument would be the request ID, which is not the case.

[santib]

Good catch, thank you!