In the install doc, added a link to the gentoo step to install Theano.

doc/install.txt

@@ -81,6 +81,12 @@ Alternative installation on Ubuntu with PPA
 
 Benjamin J. McCann provides `installation documentation <http://www.benmccann.com/dev-blog/installing-cuda-and-theano/>`_ for Ubuntu 11.04 with CUDA 4.0 PPA.
 
+Gentoo
+~~~~~~
+
+Brian Vandenberg emailed `installation instruction on Gentoo <https://groups.google.com/d/msg/theano-dev/-8WCMn2FMR0/bJPasoZXaqoJ>`.
+
+
 .. _linux_basic:
 
 Basic user install instructions