In a RAML file (used for creating API docs), you can add arbitrary content outside of the endpoints by using the documentation key, an array where each object has a title property and Markdown-formatted content property.
Example from the spec:
#%RAML 1.0
title: ZEncoder API
baseUri: https://app.zencoder.com/api
documentation:
- title: Home
content: |
Welcome to the _Zencoder API_ Documentation. The _Zencoder API_
allows you to connect your application to our encoding service
and encode videos without going through the web interface. You
may also benefit from one of our
[integration libraries](https://app.zencoder.com/docs/faq/basics/libraries)
for different languages.
- title: Legal
content: !include docs/legal.markdown
title: ZEncoder API
baseUri: https://app.zencoder.com/api
documentation:
- title: Home
content: |
Welcome to the _Zencoder API_ Documentation. The _Zencoder API_
allows you to connect your application to our encoding service
and encode videos without going through the web interface. You
may also benefit from one of our
[integration libraries](https://app.zencoder.com/docs/faq/basics/libraries)
for different languages.
- title: Legal
content: !include docs/legal.markdown
Final thoughts
Not sure why it took me ages to find this, it's right there in the first sections of the spec.