Add comment (#1248)

Summary:
Pull Request resolved: #1248

As titled. Add comment for the rules for clarity.

Reviewed By: cyrjano, vivekmig

Differential Revision: D55035875

fbshipit-source-id: 303b067df6f62e75cc0ebc9dddacea0a6344a935

Author: cicichen01

setup.cfg

@@ -1,6 +1,7 @@
 [flake8]
 # E203: black and flake8 disagree on whitespace before ':'
 # W503: black and flake8 disagree on how to place operators
+# E704: black and flake8 disagree on Multiple statements on one line (def)
 ignore = E203, W503, E704
 max-line-length = 88
 exclude =