Specify the build-system in pyproject.toml

- Needed so that "uv tool install" can work with a git url.
- pipx seemed to work without this.
- Also need to ensure that tools.toml is installed as package-data.

pyproject.toml

@@ -37,5 +37,12 @@ pydoc_color = "eris.pydoc_color:main"
 [project.urls]
 homepage = "https://github.com/ahamilton/eris"
 
+[build-system]
+requires = ["setuptools>=61.0"]
+build-backend = "setuptools.build_meta"
+
 [tool.setuptools]
 packages=["eris"]
+
+[tool.setuptools.package-data]
+"eris" = ["tools.toml"]