docs: Add links to MDUI and EntityAttributes metadata extensions from saml20-idp-hosted reference.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@3122 44740490-163a-0410-bde0-09ae8108e29a

docs/simplesamlphp-reference-idp-hosted.txt

@@ -293,6 +293,16 @@ The following options for Shibboleth 1.3 IdP's are avaiblable:
     metadata overrides the one configured in the IdP metadata.
 
 
+Metadata extensions
+-------------------
+
+SimpleSAMLphp supports generating metadata with the MDUI and EntityAttributes metadata extensions.
+See the documentation for those extensions for more details:
+
+  * [MDUI extension](./simplesamlphp-metadata-extensions-ui)
+  * [EntityAttributes](./simplesamlphp-metadata-extensions-attributes)
+
+
 Examples
 --------