Link to migration guide

Author: fhammerschmidt

markdown-pages/blog/release-12-0-0.mdx

@@ -17,6 +17,8 @@ The headline upgrades include a rewritten build system, a standalone runtime pac
 Teams upgrading from ReScript 11 should review the highlighted breaking changes and schedule time for migration.
 The new tooling provides focused commands, better diagnostics, and smaller downloads, while the language additions flatten sharp edges that many of you encountered in larger codebases.
 
+You can find the complete migration guide [here](../docs/manual/migrate-to-v12.mdx).
+
 ## Breaking Changes
 
 ### Build system redesign