Update Breadcrumbs component docs to add text length accessibility recommendation

[joshfarrant]

Summary

Updates the Breadcrumbs component's docs to add a recommendation about the maximum length of individual items based on the Accessibility Audit Guide — 1.4.10 Reflow guidance.

What should reviewers focus on?

• Check you're happy with the images and the updated copy

Supporting resources (related issues, external links, etc):

• Closes https://github.com/github/primer/issues/3755

Contributor checklist:

• All new and existing CI checks pass
• Tests prove that the feature works and covers both happy and unhappy paths
• Any drop in coverage, breaking changes or regressions have been documented above
• UI Changes contain new visual snapshots (generated by adding update snapshots label to the PR)
• All developer debugging and non-functional logging has been removed
• Related issues have been referenced in the PR description

Reviewer checklist:

• Check that pull request and proposed changes adhere to our contribution guidelines and code of conduct
• Check that tests prove the feature works and covers both happy and unhappy paths
• Check that there aren't other open Pull Requests for the same update/change

[changeset-bot]

⚠️ No Changeset found

Latest commit: bedda05

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[github-actions]

🟢 No design token changes found

[github-actions]

🟢 No visual differences found

Our visual comparison tests did not find any differences in the UI.

[rezrah]

Nice, thanks @joshfarrant