Add pyproject.toml config file for Black

With the gigantic node_modules directory, Black suddenly started taking
over 15 seconds to run (compared to less than a second before). This
gets it to skip the node_modules directory, as well as a few other ones.

tildes/pyproject.toml

@@ -0,0 +1,2 @@
+[tool.black]
+exclude = "(\\.mypy_cache|node_modules|scss|sql|static)"