[changelog] documenting previous commit.

Author: rzwitserloot

doc/changelog.markdown

@@ -2,7 +2,8 @@ Lombok Changelog
 ----------------
 
 ### v1.18.21 "Edgy Guinea Pig"
-* Added the `@StandardException` feature. [Pull Request #2702](https://github.com/projectlombok/lombok/pull/2702).
+* PLATFORM: JDK17 support added. [Issue #2898](https://github.com/projectlombok/lombok/issues/2898).
+* FEATURE: Added the `@StandardException` feature. [Pull Request #2702](https://github.com/projectlombok/lombok/pull/2702).
 * IMPROBABLE BREAKING CHANGE: If the underlying compiler and `--release` / `--source` option is 10 or higher, lombok's `val` is now replaced by `final var`. That means compound declarations such as `val x = 10, y = 12;` now fail (lombok's old `val` implementation supported it, javac's `var` does not), but IDE support in particular is more reliable. We decided it was worth the tradeoff.
 
 ### v1.18.20 (April 2nd, 2021)