Feat: Add describe() to default sketch to encourage accessibility

[yugalkaushik]

Issue:

Closes #3081

Suggestions taken from #3380

Adds describe() to the default sketch template to encourage users to make their p5.js sketches accessible from the start.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• has no typecheck errors (npm run typecheck)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123
• meets the standards outlined in the accessibility guidelines