Update example exclude to match only files in root (#1861)

* Update example exclude to match only files in root

The `exclude` section of the example `pyproject.toml` file didn't work
as expected. It claimed to exclude matched files only in the project
root, but it actually excluded matched files at any directory level
within the project. We can address this by prepending `^/` to the regex
to ensure that it only matches files in the project root.

See https://github.com/psf/black/issues/1473#issuecomment-740008873 for
explanation.

* Mention excluding directories as well

diff --git a/README.md b/README.md
index f1ec76938f01fc4ee7932958af04714b76cc57b6..83ecb89d6c9ba09687d05a7194cb5df8f3cf3b59 100644 (file)
--- a/README.md
+++ b/README.md
@@ -313,9 +313,10 @@ line-length = 88
 target-version = ['py37']
 include = '\.pyi?$'
 exclude = '''
-
-(
-  /(
+# A regex preceded with ^/ will apply only to files and directories
+# in the root of the project.
+^/(
+  (
       \.eggs         # exclude a few common directories in the
     | \.git          # root of the project
     | \.hg