Welcome files that correspond to a servlet-mapping should not be ignored. As an example, a welcome file can be defined as "index.jsf" that maps this to the faces servlet via the servlet mapping "*.jsf". The welcome file should be served when navigating to the folder.

This is as specified in the Servlet 3.0 specification (Section 10.10):

... the Web server MUST again append each welcome file in the order specified in the deployment descriptor to the partial request and check if a servlet is mapped to that request URI.

As an example of this in practice, refer to one of the many stackoverflow questions on the subject:
http://stackoverflow.com/questions/4616493/how-to-set-jsf2-welcome-file-with-faces-servlet-mapping/4618142