chore: prepare release notes for 0.24.0

Author: Midnighter

release-notes/0.24.0.md

@@ -0,0 +1,13 @@
+# Release notes for cobrapy 0.24.0
+
+## New features
+
+* Gene-protein-reaction association rules are now represented by a structured object `GPR`.
+  `Reaction.gene_reaction_rule` still returns a string and a string can be assigned
+  to it that will modify the underlying `GPR` instance.
+* The `Reaction` class has gained another attribute `Reaction.gpr` which allows direct
+  access to the `GPR` instance (#1143).
+
+## Fixes
+
+* Syntax update and type annotations (#1151).