[docs] improve documentation for enumerate() (built-in function) (issue 22725)

[ezio.melotti at gmail.com]

http://bugs.python.org/review/22725/diff/13194/Doc/library/functions.rst
File Doc/library/functions.rst (right):

http://bugs.python.org/review/22725/diff/13194/Doc/library/functions.rst#newcode361
Doc/library/functions.rst:361: Return an enumerate object which when
:term`iterated <iterable>` yields a
"which when iterated" sounds a bit weird to me.  Would it be better if
commas were added before and after "when iterated"?
The link to "iterable" could also be moved to "enumerate object", even
though it might be somewhat misleading if one expects it to link to the
documentation of the actual enumerate object.

http://bugs.python.org/review/22725/