adds text describing the upper-case keywords used in the spec

Signed-off-by: Mike Brown <[email protected]>

Author: mikebrow

README.md

@@ -16,6 +16,8 @@ Table of Contents
   - [Linux Specific Runtime](runtime-linux.md)
 - [Implementations](implementations.md)
 
+In the specifications in the above table of contents, the keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in [RFC 2119](http://tools.ietf.org/html/rfc2119) (Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997).
+
 # Use Cases
 
 To provide context for users the following section gives example use cases for each part of the spec.