tier-1: inherit from tier-x

We want tier-1 to be another consumer of tier-x, kind of like its own
top-level Fedora variant. That way, tier-1 is now a strict superset of
tier-x, just like the other variants.

README.md

@@ -42,7 +42,7 @@ There are currently 3 tiers:
   used by all image-based Fedora variants (IoT, Atomic Desktops, and CoreOS).
   Changes to this tier may be done without accounting for external users.
 
-Both **tier-1** and **tier-x** inherit from **tier-0**.
+**tier-1** inherits from **tier-x** and **tier-x** in turn inherit from **tier-0**.
 
 All non-trivial changes to **tier-0** and **tier-x** should be ACKed by at least
 one stakeholder of each Fedora variant WGs.

tier-1/manifest.yaml

@@ -2,7 +2,7 @@
 recommends: true
 
 include:
-  - ../tier-0/manifest.yaml
+  - ../tier-x/manifest.yaml
   - autoupdates.yaml
   - bootable-rpm-ostree.yaml
   - podman.yaml