Markdown style guide: Improvements

[jpmckinney]

Change this style guide's page to .md and enable the MyST-Parser extension.

• Document how to link to within-page headings
• Front Matter: Document when/how to mark orphan pages
• Directives:
  • When to use different admonitions, e.g. note, tip, see also, caution like on https://jupyterbook.org/content/myst.html
  • Use literalinclude instead of jsoninclude, if jsonpointer is empty
  • Document when to use csv-table-no-translate (and any other directives involved in translation)
  • Check for use of other directives to document
• Demonstrate MyST-Parser's key features
  • Mainly the directive syntax, including an example of a code-block inside another directive