add a section on 'Why OpenControl?'

README.md

@@ -2,6 +2,16 @@
 
 YAML schema, examples, and validators for OpenControl format. You can find the formal definitions and learn about how to do validation in the [`kwalify/`](kwalify/) folder. The examples from the Glorious (Fake) Nation of Freedonia are the complete standalone example targeted at OpenControl beginners, so we recommend looking at those first.
 
+## Why OpenControl?
+
+OpenControl refers to both the community, and the schemas defined in this repository. You might be wondering: why use the OpenControl format, rather than write control information in a word processor? In short, the OpenControl format is **compliance as code.** That means:
+
+- **Version-controllable.** Since YAML is a textual format (rather than binary), it can be version controlled alongside the code, and updated simultaneously using the same workflow (like pull requests).
+- **Structured > unstructured.** Because OpenControl is a structured format, the information is data, so it can be converted to various formats, and/or pulled into a dashboard.
+- **Inheritable.** Copying-and-pasting control statements between documents means there isn't a canonical source of information, and to keep that information up-to-date across all your System Security Plans (SSPs). OpenControl supports inheritance, meaning the platforms, policies, and [General Support Systems (GSSs)](https://csrc.nist.gov/Glossary/Term/general-support-system) that are common across multiple information systems can have their inherited/shared control information in one place, and automatically be pulled into the documentation for all the others.
+
+See also: [Compliance Masonry for the Compliance Literate](https://github.com/opencontrol/compliance-masonry/blob/master/docs/masonry-for-the-compliance-literate.md).
+
 ## Full project examples
 
 * [Freedonia](https://github.com/opencontrol/freedonia-compliance#readme)