Small official/unofficial style cleanup - missed that one.

Signed-off-by: Lukasz Gromanowski <lgromanowski@gmail.com>

manual/opencs/filters.tex

@@ -25,7 +25,7 @@ Don't be afraid though, filters are fairly intuitive and easy to use.
 \end{description}
 
 \subsubsection{Basics}
-In fact you don't need to learn everything about filters in order to use them. In fact all you need to know to achieve decent productivity
+In fact you do not need to learn everything about filters in order to use them. In fact all you need to know to achieve decent productivity
 with OpenCS is inside basics section.
 
 \subsubsection{Interface}