[DOC] Update doc of Type.may_share_memory.

doc/extending/type.txt

@@ -140,10 +140,12 @@ default values.
 
     .. method:: may_share_memory(a, b)
 
-        Optional. Only needed for DebugMode. Return True if the python
+        Optional to run, but mandatory for DebugMode. Return True if the python
         objects `a` and `b` could share memory. Return False
         otherwise. It is used to debug when Ops didn't declare memory
-        aliaing between variables. Must be a static method.
+        aliaing between variables. Can be a static method.
+        It is highly recommande to use and is mandatory for Type in Theano
+        as our buildbot run in DebugMode.
 
 For each method, the *default* is what ``Type`` defines
 for you. So, if you create an instance of ``Type`` or an