Mention that static methods cannot use this keyword

Author: Sebastien Ponce

talk/objectorientation/advancedoo.tex

@@ -7,7 +7,7 @@
     \item Sometimes we need the address of the current object
     \item Or we need to pass our address / a reference to a different entity
       (for example to implement operators, see later)
-    \item All class methods can use the keyword \cppinline{this}
+    \item All non static class methods can use the keyword \cppinline{this}
       \begin{itemize}
         \item It returns the address of the current object
         \item Its type is \cppinline{T*} in the methods of a class {\ttfamily T}