Review 'About documentation design' page

[jdbaldry]

• Update Vale linting exclusion
• Simplify some language for readability

Rest LGTM.

Closes https://github.com/grafana/writers-toolkit/issues/689

[github-actions[bot]]

Readability report

File	AutomatedReadability	ColemanLiau	FleschKincaid	FleschReadingEase	GunningFog	LIX	SMOG
docs/sources/structure/about-documentation-design/index.md	$${10.24\space\color{green}(Δ-0.03)}$$	$${13.83\space\color{red}(Δ+0.09)}$$	$${11.49\space\color{green}(Δ-0.08)}$$	$${33.87\space\color{green}(Δ+0.09)}$$	$${12.05\space\color{green}(Δ-0.31)}$$	$${43.66\space\color{green}(Δ-0.01)}$$	$${12.26\space\color{green}(Δ-0.20)}$$

View metric targets

| Metric | Range | Ideal score | | --- | --- | --- | | [AutomatedReadability](https://en.wikipedia.org/wiki/Automated_readability_index) | 6 (very easy read) to 14 (extremely difficult read) | 8 or less | | [ColemanLiau](https://en.wikipedia.org/wiki/Coleman%E2%80%93Liau_index) | 6 (very easy read) to 17 (extremely difficult read) | 9 or less | | [FleschKincaid](https://en.wikipedia.org/wiki/Flesch%E2%80%93Kincaid_readability_tests) | 6 (very easy read) to 17 (extremely difficult read) | 8 or less | | [FleschReadingEase](https://en.wikipedia.org/wiki/Flesch%E2%80%93Kincaid_readability_tests) | 100 (very easy read) to 0 (extremely difficult read) | 70 or more | | [GunningFog](https://en.wikipedia.org/wiki/Gunning_fog_index) | 6 (very easy read) to 17 (extremely difficult read) | 10 or less | | [LIX](https://en.wikipedia.org/wiki/Lix_(readability_test)) | 20 (very easy read) to 60+ (extremely difficult read) | 35 or less | | [SMOG](https://en.wikipedia.org/wiki/SMOG) | 6 (very easy read) to 17 (extremely difficult read) | 10 or less |