Please define "DST" in README

[Benjamin Kane]

Allocating DSTs is currently somewhat painful due to limitations in Rust. It is possible to have Gc pointers to DSTs, and there is a replacement for unstable Unsize coercion, but there is no support for directly allocating arbitrarily sized DSTs.

Apologies if this is a well-known acronym, but some Google searches couldn't find it. Maybe it means "dynamically sized type" like a list in Python?

Thanks!!

[TheMatten]

Try "rust dst" - these are "Dynamically Sized Types", but in a slightly different sense compared to Python: https://doc.rust-lang.org/reference/dynamically-sized-types.html