Updated Windows installation docs with instructions about how to get rid of the…

doc/install.txt

@@ -533,8 +533,8 @@ used within a MinGW Shell (not available if you only installed Python(x,y)).
         C:\Users\login>echo %PYTHONPATH%
         C:\Users\login\Theano
 
-- Create a new ``.theanorc`` text file (or ``.theanorc.txt``, which is easier
-  to create under Windows) in your user profile directory (the directory you
+- Create a new ``.theanorc`` text file (or ``.theanorc.txt``, whichever is easier
+  for you to create under Windows) in your user profile directory (the directory you
   are into when you start a new command prompt with ``cmd``), containing the
   following two lines:
 
@@ -543,6 +543,16 @@ used within a MinGW Shell (not available if you only installed Python(x,y)).
       [blas]
       ldflags =
 
+  You do not need to do the following now, because it is not usually needed, but if
+  later on, when running Theano, you see an error message that looks like:
+    *error: 'assert' was not declared in this scope*
+  then you will have to add another section:
+
+    .. code-block:: cfg
+
+      [gcc]
+      cxxflags = -IC:\MinGW\include
+
 - You are now ready to run Theano.
   It will use NumPy for dot products, which is still pretty fast (see below for
   optional instructions on how to compile your own BLAS library).