Add CHANGELOG entry for angle-bracket generic errors

Author: AaronC81

CHANGELOG.md

@@ -147,6 +147,27 @@
   is now smaller in certain cases.
   ([Surya Rose](https://github.com/GearsDatapacks))
 
+- The compiler now shows a specific syntax error when trying to use an
+  angle-bracket syntax for generic types or function definitions:
+
+  ```txt
+  error: Syntax error
+    ┌─ /src/parse/error.gleam:1:6
+    │
+  1 │ fn id<T>(x: T) { x }
+    │      ^ I was expecting `(` here.
+
+  If you were trying to define a generic function, Gleam does not use angle brackets.
+  Instead, you should write types in the parameter list with lower-case names.
+  Each unique lower-case name becomes a type variable:
+
+      fn example(arg: t) -> t
+
+  See: https://tour.gleam.run/functions/generic-functions/
+  ```
+
+  ([Aaron Christiansen](https://github.com/AaronC81))
+
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