lint: Add isort as a linter.

Author: PIG208

tools/lint

@@ -28,6 +28,9 @@ def run() -> None:
                                   description="Standard Python linter (config: .flake8)")
     linter_config.external_linter('gitlint', ['tools/lint-commits'],
                                   description="Git Lint for commit messages")
+    linter_config.external_linter("isort", ["isort"], ["py"],
+                                  description="Sorts Python import statements",
+                                  check_arg=["--check-only", "--diff"])
 
     @linter_config.lint
     def custom_py() -> int: