[Doc]: Fix SimpleFormIterator add and remove buttons snippets

[julienV]

Problem

Closes #10171

Solution

Update of the documentation

How To Test

Check the md

Additional Checks

• The PR targets master for a bugfix, or next for a feature
• The PR includes unit tests (if not possible, describe why)
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

Also, please make sure to read the contributing guidelines.

[fzaninotto]

Thanks!