* doc: doc structure edits

Updated landing page for Guides with structure from guides/README.md.
Excluded guides/README.md from doxygen build, so it only shows in GH.
Added links to docs on the main README.md.

Signed-off-by: Grzegorz Ferenc <Grzegorz.Ferenc@nordicsemi.no>

* Restyled by prettier-markdown

* misspell: add docbuild to ignored word list

Added docbuild to .wordlist.txt.

Signed-off-by: Grzegorz Ferenc <Grzegorz.Ferenc@nordicsemi.no>

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Signed-off-by: Grzegorz Ferenc <Grzegorz.Ferenc@nordicsemi.no>
Co-authored-by: Restyled.io <commits@restyled.io>