Docs: Add missing link to the 2.0 migration guide.

docs/reference/migration/index.asciidoc

@@ -17,9 +17,9 @@ As a general rule:
 See <<setup-upgrade>> for more info.
 --
 
+include::migrate_2_0.asciidoc[]
+
 include::migrate_1_x.asciidoc[]
 
 include::migrate_1_0.asciidoc[]
 
-
-