Add guidance on how to work with hugo and format titles

[lmolkova]

I hope we could do better in semconv and either automate or at least catch some of hugo and title issues during review.

A few things that could help:

1. Is there a crash course on hugo (in the context of otel.io)? E.g.

   • we have <!--- Hugo front matter used to generate the website version of this page: ---> in some cases we have it in some other cases we don't - why?
   • Is there a good link we could add to contributing.md to help with incantations like path_base_for_github_subdir ?
   • How to rename/move files keeping website links

2. Could we come up with some guidance on how to do things in semconv?
   E.g.

   • linkTitle is a short thing that does not include semconv name, just the sub-area within it. It should usually be Spans, Metrics, Resources, etc. It's in 'Sentence case'
   • Headings should use 'Title Case' (TBH I'd default to `Sentence case' everywhere)

Originally posted by @lmolkova in #1820 (review)

[lmolkova]

See also

sentence case is my preference as well, and what Google recommends in it's style guide, see Headings:

#1820 (comment)

[chalin]

By implementing #1821, I hope to simplify (1), by:

• Having every file include front matter (not in comments)
• Making path_base_for_github_subdir unnecessary -- see [editorial] Drop path_base_for_github_subdir from front matter #1846

For (2), here are some initial thoughts:

• The points you make in the opening comment about linkeTitle and the use of sentence case are relevant.
• Paths to doc pages from within /docs should not step outside of /docs only to come back in. We could test for this be reporting as an error any use of paths of the form ../docs/, but I'm not sure if there'd be any false positives (I don't think so). Cf. [editorial] Normalize path to docs from docs #1843