docs: Update website workflow docs

[Josmithr]

Based on my current work in the website space, this PR is attempting to improve / fill in workflow guidance for working with the website code (/docs).

It also adds a helper script for running documentation generation in the repo, excluding the website.

[github-actions]

🔗 Found some broken links! 💔

Run a link check locally to find them. See
https://github.com/microsoft/FluidFramework/wiki/Checking-for-broken-links-in-the-documentation for more information.

linkcheck output

> fluidframework-docs@0.25.0 linkcheck /home/runner/work/FluidFramework/FluidFramework/docs
> npm run linkcheck:fast -- --external


> fluidframework-docs@0.25.0 linkcheck:fast /home/runner/work/FluidFramework/FluidFramework/docs
> linkcheck http://localhost:1313 --skip-file skipped-urls.txt "--external"

Crawling...

http://localhost:1313/css/style.min.f22f6c22fcc37a0d857a17c9c1202a67c28deef90cc26a52b7539b903f623331.css
- (1:1031) url(...) => https://c.s-microsoft.com/static/fonts/segoe-ui/west-european/light/latest.svg (HTTP 503)
- (1:1184) url(...) => https://c.s-microsoft.com/static/fonts/segoe-ui/west-european/semilight/latest.eot (HTTP 503)
- (1:1272) url(...) => https://c.s-microsoft.com/static/fonts/segoe-ui/west-european/semilight/latest.eot? (HTTP 503)
- (1:1740) url(...) => https://c.s-microsoft.com/static/fonts/segoe-ui/west-european/semilight/latest.svg (HTTP 503)
- (1:3130) url(...) => https://c.s-microsoft.com/static/fonts/segoe-ui/west-european/semibold/latest.svg (HTTP 503)
- (1:3286) url(...) => https://c.s-microsoft.com/static/fonts/segoe-ui/west-european/bold/latest.eot (HTTP 503)

http://localhost:1313/docs/apis/core-interfaces/ifluidcodedetailscomparer
- (873:360) 'Array.sort' => https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort#Description (HTTP 200 but missing anchor)
- (877:168) 'https://..' => https://github.com/npm/node-semver#usage (HTTP 200 but missing anchor)
- (885:25) 'Array.sort' => https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort#Description (HTTP 200 but missing anchor)
- (914:25) 'https://..' => https://github.com/npm/node-semver#usage (HTTP 200 but missing anchor)

http://localhost:1313/docs/apis/core-interfaces/ifluidcodedetailscomparer/
- (873:360) 'Array.sort' => https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort#Description (HTTP 200 but missing anchor)
- (877:168) 'https://..' => https://github.com/npm/node-semver#usage (HTTP 200 but missing anchor)
- (885:25) 'Array.sort' => https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort#Description (HTTP 200 but missing anchor)
- (914:25) 'https://..' => https://github.com/npm/node-semver#usage (HTTP 200 but missing anchor)


Summary of most serious issues:

http://localhost:1313/css/style.min.f22f6c22fcc37a0d857a17c9c1202a67c28deef90cc26a52b7539b903f623331.css
- (1:1031) url(...) => https://c.s-microsoft.com/static/fonts/segoe-ui/west-european/light/latest.svg (HTTP 503)
- (1:1184) url(...) => https://c.s-microsoft.com/static/fonts/segoe-ui/west-european/semilight/latest.eot (HTTP 503)
- (1:1272) url(...) => https://c.s-microsoft.com/static/fonts/segoe-ui/west-european/semilight/latest.eot? (HTTP 503)
- (1:1740) url(...) => https://c.s-microsoft.com/static/fonts/segoe-ui/west-european/semilight/latest.svg (HTTP 503)
- (1:3130) url(...) => https://c.s-microsoft.com/static/fonts/segoe-ui/west-european/semibold/latest.svg (HTTP 503)
- (1:3286) url(...) => https://c.s-microsoft.com/static/fonts/segoe-ui/west-european/bold/latest.eot (HTTP 503)


Stats:
  121051 links
    1316 destination URLs
       1 URLs ignored
       8 warnings
       6 errors

[alpaix]

lgtm

[github-actions]

This commit is queued for merging with the next branch! Please ignore this PR for now. Contact @microsoft/fluid-cr-infra for help.