Add ruling about source code encodings.

pep-0008.txt

@@ -124,6 +124,17 @@ Code lay-out
     characters as page separators, so you may use them to separate
     pages of related sections of your file.
 
+  Encodings (PEP 263)
+
+    Code in the core Python distribution should aways use the ASCII or
+    Latin-1 encoding (a.k.a. ISO-8859-1).  Files using ASCII should
+    not have a coding cookie.  Latin-1 should only be used when a
+    comment or docstring needs to mention an author name that requires
+    Latin-1; otherwise, using \x escapes is the preferred way to
+    include non-ASCII data in string literals.  An exception is made
+    for those files that are part of the test suite for the code
+    implementing PEP 263.
+
 
 Imports