Accessibility audit is flagging markup errors

[barrymcgee]

What article on docs.github.com is affected?

• Homepage
• All article pages

What part(s) of the article would you like to see updated?

• Links which are aria-hidden are keyboard accessible
• Page headings do not always increment by one
• Page elements exist outside of roles
• The navigation in the sidebar contains invalid nested unordered lists
• There is more than one <main> element on individual article pages

[welcome]

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