docs(button): update button description

[linstedt]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (yarn build) was run locally and any changes were pushed
• Unit tests (yarn test) were run locally and passed
• Visual Regression Tests (yarn visual-regression) were run locally and passed
• Linting (npm lint) was run locally and passed

Pull request type

Please check the type of change your PR introduces:

• Bug fix
• Feature
• Refactoring (no functional changes, no API changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

GitHub Issue Number: N/A

What is the new behavior?

Does this introduce a breaking change?

• Yes
• No

Testing

Other information

Open Questions:

• Icon button with icon size 32px available in components but not in Styleguide - do we need this variant?
• Icon button shapes: Currently, some components don't follow the rules described here (e.g. clear button in search field) - should it be fixed?
• Button group: What button variants are available? Is there always at least one primary button? Or is that the selected one?

[linstedt]

@danielleroux @nuke-ellington We would like to add a code example on the top to give an interactive example for each description. Silvio had some feedback coming in about the lack of theming of the illustrations, this could be a small work around. What do you think?

[nuke-ellington]

Made some suggestions to the text

[nuke-ellington]

lgtm