Add note about security domain restriction for webservices subsystem

In current webservice elytron integration, the security domain specified to secure webservice endpoint must be the same name with elytron security domain name .
Reference https://developer.jboss.org/message/977744#977744

This configuration in undertow makes webservices deployment unaware of the desired "new-name" security domain

<application-security-domains>
    <application-security-domain name="new-name" security-domain="original-name"/>
</application-security-domains>

while this causes "original-name" to be visible just fine

<application-security-domains>
    <application-security-domain name="original-name" security-domain="original-name"/>
</application-security-domains>

asoldano or jimma could provide more details here about what exactly should be in documentation.