add migration readme and readme-pre to link to migration

Author: doebrowsk

Migration-Scripts/Legacy-IIS/LegacyIISMigrationGuide.md renamed to Migration-Scripts/Legacy-IIS/readme.md

@@ -0,0 +1,5 @@
+### Migrating Legacy IIS Stores
+If you have existing IIS stores with the built-in IIS types, and plan to upgrade to Keyfactor Command 11 or later, you will need to migrate from the legacy store types to the IISU and WinCert store type defined in this repository.
+
+You can find the guide and migration scripts in this repository, located here:
+[Legacy IIS Migration](./Migration-Scripts/Legacy-IIS)