Add DOS-CGA Color Scheme

[fnky]

Please provide the following information:

• Link to your code repository: https://github.com/fnky/dos-cga-theme
• Link to the tags page with at least one semver tag: https://github.com/fnky/dos-cga-theme/releases/tag/0.1.0

Also make sure you:

• Used "tags": true and not "branch": "master" (versioning docs)
• Ran the tests (tests docs)

[FichteFoll]

You might want to use the proper term ("color scheme") in your readme also. If you want to rename the repo on github as well, you will need to adjust the url in a new PR.