docs: Add link to expirycheck.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@2977 44740490-163a-0410-bde0-09ae8108e29a

docs/simplesamlphp-authproc.txt

@@ -141,6 +141,7 @@ The following filters are included in the simpleSAMLphp distribution:
 - [`core:StatisticsWithAttribute`](./core:authproc_statisticswithattribute): Create a statistics logentry.
 - [`core:TargetedID`](./core:authproc_targetedid): Generate the `eduPersonTargetedID` attribute.
 - [`core:WarnShortSSOInterval`](./core:authproc_warnshortssointerval): Give a warning if the user logs into the same SP twice within a few seconds.
+- ['expirycheck:ExpiryDate`](./expirycheck:expirycheck): Block access to accounts that have expired.
 - [`preprodwarning:Warning`](./preprodwarning:warning): Warn the user about accessing a test IdP.
 - [`saml:AttributeNameID`](./saml:nameid): Generate custom NameID with the value of an attribute.
 - [`saml:NameIDAttribute`](./saml:nameidattribute): Create an attribute based on the NameID we receive from the IdP.