Add reasons for ignores

setup.cfg

@@ -5,8 +5,12 @@ filename = *.py, *.pyx
 ignore = E501, W503
 # E225: Missing whitespace around operator
 # E226: Missing whitespace around arithmetic operator
-# E227: Missing whitespace around bitwise or shift operator
+# E227: Missing whitespace around bitwise or shift operator (flake8 will complain
+# for the pointers (treated as multiplication operator in python) and
+# address-of (&) operator (bitwise and operator in python))
 # E266: Too many leading '#' for block comment
-# E402: Module level import not at top of file
+# E402: Module level import not at top of file (flake8 treats the cimports as
+# non-import code and thus complains about the subsequent imports as imports not
+# being on the top)
 # E999: SyntaxError
 per_file_ignores = gdist.pyx: E225, E226, E227, E266, E402, E999