Add and fix redirects

Author: crandmck

docs/prod-cert-redirect.mdx

@@ -0,0 +1,10 @@
+---
+id: prod-cert
+title: Redirect
+---
+
+import { Redirect } from '@docusaurus/router';
+
+<Redirect to="signing/prod-cert/" />
+
+This page will be redirected to `https://opensource.contentauthenticity.org/docs/signing/prod-cert`.

docs/signing-manifests-redirect.mdx

@@ -5,6 +5,6 @@ title: Redirect
 
 import { Redirect } from '@docusaurus/router';
 
-<Redirect to="signing/signing-certs" />
+<Redirect to="../signing/" />
 
 This page will be redirected to `https://opensource.contentauthenticity.org/docs/manifest/signing-manifests`.