[ReadMe] Adds boilerplate MUST, MAY, etc. language

Signed-off-by: Rob Dolin <[email protected]>

Author: RobDolinMS

README.md

@@ -4,6 +4,8 @@ The OCI Image Format project creates and maintains the software shipping contain
 
 This specification defines how to create an OCI Image, which will generally be done by a build system, and output an [image manifest](manifest.md), a [filesystem serialization](serialization.md), and an [image configuration](serialization.md#image-json-description). At a high level the image manifest contains metadata about the contents and dependencies of the image including the content-addressable identity of one or more filesystem serialization archives that will be unpacked to make up the final runnable filesystem. The image configuration includes information such as application arguments, environments, etc. The combination of the image manifest, image configuration, and one or more filesystem serializations is called the "OCI Image".
 
+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).
+
 ![](img/build-diagram.png)
 
 Once built the OCI Image can then discovered by name, downloaded, verified by hash, trusted through a signature, and unpacked into an [OCI Runtime Bundle](https://github.com/opencontainers/runtime-spec/blob/master/bundle.md).