[skip changelog] Add links to additional information in the examples section of the library specification

[per1234]

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?

Documentation update.

• What is the current behavior?

Sources of additional information about the example sketches of libraries are not readily available to library authors.

• What is the new behavior?

Links to additional information are provided in the relevant section of the Arduino library specification.

• Does this PR introduce a breaking change?

No.