add meta-optimizer info in conv doc

doc/library/tensor/nnet/conv.txt

@@ -22,7 +22,7 @@
 .. moduleauthor:: LISA
 
 
-The recomanded user interface are:
+The recommended user interface are:
 
 - :func:`theano.tensor.nnet.conv2d` for 2d convolution
 - :func:`theano.tensor.nnet.conv3d` for 3d convolution
@@ -42,7 +42,7 @@ Either cuDNN and the gemm version can be disabled using the Theano flags
 respectively. If both are disabled, it will raise an error.
 
 
-For the cuDNN version, there are different algorythms with different
+For the cuDNN version, there are different algorithms with different
 memory/speed trade-offs. Manual selection of the right one is very
 difficult as it depends on the shapes and hardware. So it can change
 for each layer. An auto-tuning mode exists and can be activated by
@@ -56,6 +56,15 @@ slower as it tries and times each implementation it has. So if you
 benchmark, it is important that you remove the first call from your
 timing.
 
+Also, a meta-optimizer has been implemented for the gpu convolution
+implementations to automatically choose the fastest implementation
+for each specific convolution in your graph. For each instance, it will
+compile and benchmark each applicable implementation and choose the
+fastest one. It can be enabled using ``optimizer_including=conv_meta``.
+The meta-optimizer can also selectively disable cudnn and gemm version
+using the Theano flag ``metaopt.optimizer_excluding=conv_dnn`` and
+``metaopt.optimizer_excluding=conv_gemm`` respectively.
+
 
 .. note::