refactor: move fallback theme from config to theme parser

wowchemy/layouts/index.html

@@ -1,9 +1,10 @@
 {{- define "main" -}}
 
 {{/* Check that user fully installed Wowchemy. */}}
-{{ if not (isset site.Params "theme") }}
-  {{ errorf "Please complete the installation of Wowchemy by following the steps at https://wowchemy.com/docs/install/" }}
-{{ end }}
+{{/* Commented out to allow user to have no params.yaml and just use the defaults. */}}
+{{/* if not (isset site.Params "seo") */}}
+  {{/* errorf "Please complete the installation of Wowchemy by following the steps at https://wowchemy.com/docs/install/" */}}
+{{/* end */}}
 
 {{/* Deprecation warnings */}}