Don't limit black to git/

This changes the documentation in README.md to recommend running
"black ." and changes the command to that in tox.ini, so that more
paths are covered (in practice, test/ and setup.py).

Author: EliahKagan

README.md

@@ -159,7 +159,7 @@ mypy -p git
 For automatic code formatting, run:
 
 ```bash
-black git
+black .
 ```
 
 Configuration for flake8 is in the `./.flake8` file.

tox.ini

@@ -23,7 +23,7 @@ ignore_outcome = true
 [testenv:black]
 description = Check style with black
 base_python = py39
-commands = black --check --diff git
+commands = black --check --diff .
 
 # Run "tox -e html" for this. It is deliberately excluded from env_list, as
 # unlike the other environments, this one writes outside the .tox/ directory.