Improve changelog

Author: penelopeysm

HISTORY.md

@@ -3,7 +3,7 @@
 ## Optimisation interface
 
 The Optim.jl interface has been removed (so you cannot call `Optim.optimize` directly on Turing models).
-You can use the `maximum_likelihood` or `maximum_a_posteriori` functions with an Optim.jl solver instead (which goes via Optimization.jl).
+You can use the `maximum_likelihood` or `maximum_a_posteriori` functions with an Optim.jl solver instead (via Optimization.jl: see https://docs.sciml.ai/Optimization/stable/optimization_packages/optim/ for documentation of the available solvers).
 
 ## Internal changes