Clarify that we encourage type-piracy

Author: timholy

README.md

@@ -9,6 +9,12 @@ This package represents intervals of an ordered set. For an interval
 spanning from `a` to `b`, all values `x` that lie between `a` and `b`
 are defined as being members of the interval.
 
+This package is intended to implement a "minimal" foundation for
+intervals upon which other packages might build. In particular, we
+*encourage* "type-piracy" (developing new operations for the interval
+types defined here), for the reason that only one interval package can
+unambiguously define the `..` and `±` operators (see below).
+
 Currently this package defines one concrete type, `ClosedInterval`.
 These define the closed set spanning from `a` to `b`, meaning the
 interval is defined as the set `{x}` satisfying `a ≤ x ≤ b`. This is