Updates to "breadcrumbs" & links in docs pages

[jay-khatri]

Task 1: links to headings

For our docs, we don't render the index.md doc in the left panel by design. For example, there is no way to get to https://www.highlight.io/docs/general/company from the left sidebar here:

However, by clicking the link, the page still exists.

We should handle this by redirecting this ^ link to the first child of the heading. In this case, we should redirect https://www.highlight.io/docs/general/company to https://www.highlight.io/docs/general/company/values.

Task 2: breadcrumbs

As a second step, we should make these breadcrumbs clickable. Given the above change, this will mean that clicking on "Company" and "Mission & Values" should take you to the same place.

[jay-khatri]

cc @ccschmitz if you have anything to add. Thanks for reminding of this today.

[ccschmitz]

We should handle this by redirecting this ^ link to the first child of the heading. In this case, we should redirect https://www.highlight.io/docs/general/company to https://www.highlight.io/docs/general/company/values.

Might be worth trying to hide these in our search results as well, otherwise we show a few options for language/framework searches and it's not clear where to start.

[Crawron]

Fixed in #416