Docs: Readdress Implementations Page

[danehans]

This page in the docs contains a list of implementations. All implementations include a conformance report at various GIE release versions. Should this page state that an implementation must be conformant to be listed here? If so, update the page to be explicit and link to the top-level gateway conformance report page.

[danehans]

This page has not been updated since the early stages of the project, so I'm a +1 now that the project has matured and contains multiple conformant implementations.