Give also hint about possible conflicts in the user_webdavauth description

apps/user_webdavauth/appinfo/info.xml

@@ -2,7 +2,9 @@
 <info>
 	<id>user_webdavauth</id>
 	<name>WebDAV user backend</name>
-	<description>Authenticate users by a WebDAV call. You can use any WebDAV server, ownCloud server or other webserver to authenticate. It should return http 200 for right credentials and http 401 for wrong ones.</description>
+	<description>Authenticate users by a WebDAV call. You can use any WebDAV server, ownCloud server or other webserver to authenticate. It should return http 200 for right credentials and http 401 for wrong ones.
+
+	This app is not compatible to the LDAP user and group backend.</description>
 	<licence>AGPL</licence>
 	<author>Frank Karlitschek</author>
 	<require>4.9</require>