add Changelog topic to bootstrap/README.md

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

Author: onur-ozkan

Diff for: src/bootstrap/README.md

@@ -182,9 +182,27 @@ Some general areas that you may be interested in modifying are:
   `Config` struct.
 * Adding a sanity check? Take a look at `bootstrap/sanity.rs`.
 
+If you make a major change on bootstrap configuration, please remember to:
+
++ Update `CONFIG_CHANGE_HISTORY` in `src/bootstrap/lib.rs`.
+* Update `change-id = {pull-request-id}` in `config.example.toml`.
+
+A 'major change' includes
+
+* A new option or
+* A change in the default options.
+
+Changes that do not affect contributors to the compiler or users
+building rustc from source don't need an update to `CONFIG_CHANGE_HISTORY`.
+
 If you have any questions, feel free to reach out on the `#t-infra/bootstrap` channel
 at [Rust Bootstrap Zulip server][rust-bootstrap-zulip]. When you encounter bugs,
 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`.