roadmap: update links and add wiki reference

Signed-off-by: Vincent Batts <[email protected]>

Author: vbatts

README.md

@@ -26,7 +26,7 @@ To provide context for users the following section gives example use cases for e
 
 # Releases
 
-There is a loose [Road Map](https://github.com/opencontainers/specs/wiki/RoadMap:) on the wiki.
+There is a loose [Road Map](./ROADMAP.md).
 During the `0.x` series of OCI releases we make no backwards compatibility guarantees and intend to break the schema during this series.
 
 # Contributing

ROADMAP.md

@@ -6,6 +6,8 @@ The items in the 1.0 roadmap can be broken down into smaller milestones that are
 The topics below are broad and small working groups will be needed for each to define scope and requirements or if the feature is required at all for the OCI level.
 Topics listed in the roadmap do not mean that they will be implemented or added but are areas that need discussion to see if they fit in to the goals of the OCI.
 
+Listed topics may defer to the [project wiki](https://github.com/opencontainers/specs/wiki/RoadMap:) for collaboration.
+
 ## 1.0
 
 ### Digest and Hashing