Add 2020 roadmap 🛣️

In tektoncd/community#77 we started on a roadmap
for 2020 for all of Tekton but folks pointed out it makes more sense to
let each project's own roadmap live in the repo with them.

roadmap.md

@@ -0,0 +1,21 @@
+# Tekton Catalog Roadmap
+
+This doc describes the roadmap for [the Tekton Catalog](https://github.com/tektoncd/catalog).
+
+The catalog is a key piece of
+[Tekton's mission](https://github.com/tektoncd/community/blob/master/roadmap.md#mission-and-vision).
+In 2019 we got a solid start on a catalog of reusable `Tasks` and in 2020 we want to keep this momentum
+going and make the catalog even more useful by adding:
+
+* [Component versioning](https://github.com/tektoncd/pipeline/issues/1839)
+* Clear indications of which versions of Tekton Pipelines (and Triggers) a component
+  is compatible with
+* A clear story around ownership of components
+* [Support for custom catalogs](https://docs.google.com/document/d/1O8VHZ-7tNuuRjPNjPfdo8bD--WDrkcz-lbtJ3P8Wugs/edit#)
+* Support for more components, e.g. `Pipelines` and `TriggerTemplates` in
+  addition to `Tasks`
+* Increased confidence in component quality through:
+  * Clear testing requriements
+  * Support for testing components that depend on external services
+* Increased documentation and examples
+* Well defined Tekton API conformance