More clarification and numpydoc fixes

doc/library/gradient.txt

@@ -14,8 +14,8 @@
    from theano.gradient import *
 
 Symbolic gradient is usually computed from :func:`gradient.grad`, which offers a
-more convenient syntax for the common case of wanting the gradient in some
-expressions with respect to a scalar cost.  The :func:`grad_sources_inputs`
+more convenient syntax for the common case of wanting the gradient of some
+scalar cost with respect to some input expressions. The :func:`grad_sources_inputs`
 function does the underlying work, and is more flexible, but is also more
 awkward to use when :func:`gradient.grad` can do the job.