feat: initial commit of wdl-doc documentation page style

[claymcleod]

This PR adds a basic style scaffold for producing the CSS file used in wdl-doc. Styles can be added in the src folder and compiled into development (pnpm run dev, watches the directory and serves the example.html file live) or production (pnpm run prod, which needs a subsequent pnpm run serve to serve the example.html file).

You can update the example.html file with a fully-featured generated page that we can test with.

• Please use pnpm, as it's way better than npm in my experience.

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