Update blueprints.rst - Error Handlers

Added information about custom error handlers in Blueprints with example based simple_page.

docs/blueprints.rst

@@ -202,3 +202,18 @@ you can use relative redirects by prefixing the endpoint with a dot only::
 
 This will link to ``admin.index`` for instance in case the current request
 was dispatched to any other admin blueprint endpoint.
+
+Error Handlers
+--------------
+
+Blueprints support the errorhandler decorator just like the :class:`Flask`
+application object, so it is easy to make Blueprint-specific custom error
+pages.
+
+Here is an example for a "404 Page Not Found" exception::
+
+    @simple_page.errorhandler(404)
+    def page_not_found(e):
+        return render_template('pages/404.html')
+
+More information on error handling see :ref:`errorpages`.