nnet.conv - added comments to file __doc__

theano/tensor/nnet/conv.py

 """
-Contains an op for convolving input images with a set of filters. This was
+Contains an Op for convolving input images with a set of filters. This was
 developed especially for Convolutional Neural Networks.
+
+For related ops, including downsampling and subsampling, see
+tensor.signal and tensor.signal.downsample.
+
+See especially conv2d().
 """
 
 __docformat__ = "restructuredtext en"