Document the callout styles (missing), adding the 3 new ones in UI-Kit

[klepas]

Housekeeping

• There isn't another issue already open for this problem/need.
• I’ve identified or assigned this issue to someone who I think can help.

What do you need?

• Document the callout styles
• Add the 3 new ones added to UI-Kit:
  1. callout--info
  2. callout--error
  3. callout--success

These new ones were added in this PR: AusDTO/gov-au-ui-kit#449

The HTML for the example was added in AusDTO/gov-au-ui-kit#452

Which entry/section is this related to?

Probably Patterns? I looked up the IA spreadsheet doc to see where the callouts landed:

Additional information (optional)

See design clinic trello card: https://trello.com/c/zlVEjY76/2-form-validation

[klepas]

PR up ^.

[joolswood]

See comment #124 (comment)