Update HISTORY.md

Co-authored-by: Markus Hauru <[email protected]>

Author: penelopeysm

HISTORY.md

@@ -8,6 +8,7 @@ These functions check whether a given `VarName` has a value in the given `NamedT
 
 The optional `Distribution` argument allows one to reconstruct a full value from its component indices.
 For example, if `container` has `x[1]` and `x[2]`, then `hasvalue(container, @varname(x), dist)` will return true if `size(dist) == (2,)` (for example, `MvNormal(zeros(2), I)`).
+In this case plain `hasvalue(container, @varname(x))` would return `false`, since we can not know whether the vector-valued variable `x` has all of its elements specified in `container` (there might be an `x[3]` missing).
 
 These functions (without the `Distribution` argument) were previously in DynamicPPL.jl (albeit unexported).