Fix doc warning

doc/faq.txt

@@ -43,6 +43,8 @@ CPUs. In fact, Theano asks g++ what are the equivalent flags it uses, and re-use
 them directly.
 
 
+.. _faster-theano-function-compilation:
+
 Faster Theano Function Compilation
 ----------------------------------
 

doc/tutorial/modes.txt

@@ -226,7 +226,7 @@ stabilize          "+++++"       "++"            Only applies stability opts
 
 For a detailed list of the specific optimizations applied for each of these
 optimizers, see :ref:`optimizations`. Also, see :ref:`unsafe_optimization` and
-:ref:`faster-theano-function-compilation`.
+:ref:`faster-theano-function-compilation` for other trade-off.
 
 
 .. _using_debugmode: