add ssort to readme

README.md

@@ -138,6 +138,8 @@ good idea!
   the source code in the `src/` folder. We want this to stay at 10/10!
 - [isort](https://pycqa.github.io/isort/index.html) via `isort src/` to make
   sure that imports are in a standard order (black doesn't do this).
+- [ssort](https://github.com/bwhmather/ssort) via `ssort src/` to better group
+  code.
 - `pip freeze` to figure out which versions of depencencies to use in
   `pyproject.toml`. This is only necessary if you're adding or removing a new
   dependency to the project.