add note about _apex_index in FAQ
add note about _apex_index in FAQ

ianrtracey/apex,llun/apex,ianrtracey/apex,DaveBlooman/apex,DaveBlooman/apex,apex/apex,ianrtracey/apex,apex/apex,ianrtracey/apex,apex/apex,ianrtracey/apex,apex/apex,DaveBlooman/apex,DaveBlooman/apex,apex/apex,DaveBlooman/apex,llun/apex,llun/apex,apex/apex,ianrtracey/apex,llun/apex,apex/apex,llun/apex,DaveBlooman/apex,llun/apex