Add German rules

[eveiscoull]

Rules for the German language are needed to ensure multiple languages are covered by Doclint.

[eveiscoull]

There's some general rules that can be translated because they're language-agnostic:

• DOC-EN02: Use simple language
• DOC-EN03: Use generic terms
• DOC-EN04: Organize content with headings
• DOC-EN14: Avoid double sounds
• DOC-EN15: Write instructions from a user's perspective
• DOC-EN16: Limit minor steps or instructions to a maximum of 3