The `ChangeLog` is included in the official releases, it's generated from the Git log during `make dist`.
If you don't want to compile Geany first, you can run `git log` from within the Git source tree.
If you don't want to even check-out the Git source tree, you can [browse the history online](https://github.com/geany/geany/commits/master).
Finally, every release is accompanied by release notes which highlight the most important changes between versions and are included in the [`NEWS` file](https://raw.githubusercontent.com/geany/geany/master/NEWS) and can also be viewed through [Github releases](https://github.com/geany/geany/releases) or on [the Geany website](https://www.geany.org/documentation/releasenotes/).