Link Recommendation Track etc. in Interop 2026 proposal templates

Suggested by @jsnkuhn in https://github.com/web-platform-tests/interop/issues/589#issuecomment-1929665846.

The action would be to link [Recommendation Track](https://www.w3.org/policies/process/#rec-track) in the templates which we removed in https://github.com/web-platform-tests/interop/pull/862/files when we revive them for Interop 2026.