Arduino IDE and Arduino Web Editor use the term "sketchbook", while Arduino CLI and Arduino Pro IDE use the term "user directory". In order for the documentation to be friendly to all users of Arduino's development software, both terms must be used in the documentation.

Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests before creating one)
• The PR follows our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce?

docs update

• What is the current behavior?

In a couple places, the documentation uses only the term "sketchbook". Arduino IDE and Arduino Web Editor use the term "sketchbook", while Arduino CLI and Arduino Pro IDE use the term "user directory". In order for the documentation to be friendly to all users of Arduino's development software, both terms must be used.

• What is the new behavior?

"User directory" is always mentioned in conjunction with the use of the term "sketchbook" in the documentation.

• Does this PR introduce a breaking change?

No