Add require note to CHANGELOG, closes #15077

Author: josevalim

CHANGELOG.md

@@ -195,7 +195,13 @@ The type system was made possible thanks to a partnership between [CNRS](https:/
   * [mix compile] Enforce `:elixirc_paths` to be a list of strings to avoid paths from being discarded (the only documented type was lists of strings)
   * [mix test] Add `mix test --dry-run`
 
-### 2. Hard deprecations
+### 2. Potential breaking changes
+
+#### Elixir
+
+  * `require SomeModule` no longer expands to the given module at compile-time, but it still returns the module at runtime. Note that while Elixir does not guarantee macros will expand to certain constructs, but since this can break code relying on the previous behaviour, such as `require(SomeMod).some_macro()`, we are adding this note to the release notes
+
+### 3. Hard deprecations
 
 #### Elixir