Create untranslated section of guidelines

[ahankinson]

Some files should be included in the guidelines verbatim, and not part of the translations.

Specifically, things like instrument names -- there will be one file that gives the instrument name in all languages, and then the preferred term for english.

The initial proposal is to create a section for these files in the guidelines.yml, and store these markdown files outside of the translated content (default/en, etc.). When Muscat pulls the Markdown files in and creates the guidelines from the .yml file, it will then pull these additional files from a separate location.

[ahankinson]

Assigned @xhero because he will probably need to help decide on the best way to address this.