clarify the role of non-determinism for float in const

Author: RalfJung

text/0000-float-semantics.md

@@ -16,6 +16,7 @@ And there is a caveat: while IEEE specifies that float operations can never outp
 That means the only way to ever see a signaling NaN in a program is to create one with `from_bits` (or equivalent unsafe operations).
 
 Floating-point operations at compile-time follow the same specification. In particular, since operations are non-deterministic, the same operation can lead to different bit-patterns when executed at compile-time (in a `const` context) vs at run-time.
+Of course, the compile-time interpreter is still deterministic. It is entirely possible to implement a non-deterministic language on a deterministic machine, by simply making some fixed choices. However, we will not specify a particular choice, and we will not guarantee it to remain the same in the future.
 
 # Motivation
 [motivation]: #motivation