Update README.md (#179)

Author: robertoschwald

README.md

@@ -30,6 +30,7 @@ One popular approach is to have a root changelog named changlog.groovy (or chang
 * Grails 2: http://grails-plugins.github.io/grails-database-migration/docs/manual/index.html
 * Grails 3 (Hibernate 4): http://grails-plugins.github.io/grails-database-migration/2.0.x/index.html
 * Grails 3/4 (Hibernate 5): http://grails-plugins.github.io/grails-database-migration/3.0.x/index.html
+* Snapshot (master): http://grails-plugins.github.io/grails-database-migration/snapshot/index.html
 
 
 ## Package distribution