docs: checklists: Codec functions must take a message struct

Some reasoning is provided as well.

Change-Id: Ic0fc7ff16b58ceff3a1ab8c08923b16de4353e33
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
diff --git a/docs/checklists/changes.md b/docs/checklists/changes.md
index 6ee0e38..5cacf3a 100644
--- a/docs/checklists/changes.md
+++ b/docs/checklists/changes.md
@@ -94,6 +94,15 @@
 
 ## Adding a new API
 
+- [ ] My new public message codec functions take a `struct` representing the
+      message as a parameter
+
+  - Function prototypes must _not_ decompose the message to individual
+    parameters. This approach is not ergonomic and is difficult to make
+    type-safe. This is especially true for message decoding functions which must
+    use pointers for out-parameters, where it has often become ambiguous whether
+    the underlying memory represents a single object or an array.
+
 - [ ] My new public `struct` definitions are _not_ marked
       `__attribute__((packed))`