Update 0.6 release notes

docs/docs/the-marten-project/release-notes/0.6.md

@@ -22,6 +22,7 @@ _Under development._
 #### Models and databases
 
 * [Query sets](../../models-and-databases/queries.md) now support XOR operations when [performing complex queries involving `q` expressions](../../models-and-databases/queries.md#complex-filters-with-q-expressions). Additionally, combining query sets using the XOR operator (`^`) is now also supported (see [`#^ (XOR)`](../../models-and-databases/reference/query-set.md#-xor)).
+* A new [`slugify`](../../models-and-databases/reference/fields.md#slugify) option was added to [`slug`](../../models-and-databases/reference/fields.md#slug) model fields in order to make it possible to automatically generate a slug value from another local model field.
 
 #### Handlers and HTTP