show how to exclude individual files in the exclude example (#663)

* show how to exclude individual files in the exclude example

* include comments in the regex

README.md

@@ -572,9 +572,11 @@ line-length = 88
 py36 = true
 include = '\.pyi?$'
 exclude = '''
-/(
+
-    \.eggs
+(
-  | \.git
+  /(
+      \.eggs         # exclude a few common directories in the
+    | \.git          # root of the project
     | \.hg
     | \.mypy_cache
     | \.tox
@@ -583,13 +585,11 @@ exclude = '''
     | buck-out
     | build
     | dist
-
+  )/
-  # The following are specific to Black, you probably don't want those.
+  | foo.py           # also separately exclude a file named foo.py in
-  | blib2to3
+                     # the root of the project
-  | tests/data
+)
-)/
 '''
-```
 
 </details>