Introduction and relationship with MPLS

[italobusi]

I think that you need, somewhere, an explanation of the intersection of TE, MPLS and topology, starting from somewhere - hard to know where - and covering the field.

See: https://mailarchive.ietf.org/arch/msg/teas/F70NXhVah2kI3AoN4WNoqTyjaS0/

Moreover, I have received some offline comments that the current text seems implying that MPLS-TE is different than MPLS so it may be better to clarify the relationship between the different terms