add Changelog topic to bootstrap/README.md

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

src/bootstrap/README.md

@@ -188,3 +188,8 @@ please file issues on the [Rust issue tracker][rust-issue-tracker].
 
 [rust-bootstrap-zulip]: https://rust-lang.zulipchat.com/#narrow/stream/t-infra.2Fbootstrap
 [rust-issue-tracker]: https://github.com/rust-lang/rust/issues
+
+## Changelog
+
+Because we do not release bootstrap with versions, we also do not maintain CHANGELOG files. To
+review the changes made to bootstrap, simply run `git log --no-merges --oneline -- src/bootstrap`.