Mention the improvements of #87 in the changelog and documentation too.

docs/changelog.rst

@@ -1,6 +1,12 @@
 Changelog
 ==========
 
+In git master
+-------------
+
+* Added ``pk_regex`` to the ``PolymorphicParentModelAdmin`` to support non-integer primary keys.
+
+
 Version 0.5.5 (2014-04-29)
 --------------------------
 

polymorphic/admin.py

@@ -103,6 +103,9 @@ class PolymorphicParentModelAdmin(admin.ModelAdmin):
     add_type_template = None
     add_type_form = PolymorphicModelChoiceForm
 
+    #: The regular expression to filter the primary key in the URL.
+    #: This accepts only numbers as defensive measure against catch-all URLs.
+    #: If your primary key consists of string values, update this regular expression.
     pk_regex = '(\d+)'