Describe Charset.__repr__().

Doc/lib/emailcharsets.tex

@@ -177,6 +177,7 @@ standard operations and built-in functions.
 
 \begin{methoddesc}[Charset]{__str__}{}
 Returns \var{input_charset} as a string coerced to lower case.
+\method{__repr__()} is an alias for \method{__str__()}.
 \end{methoddesc}
 
 \begin{methoddesc}[Charset]{__eq__}{other}