DOC: update extended bands option for ImageWriter

Documentation/SoftwareGuide/Latex/ReadWrite.tex

@@ -369,6 +369,26 @@ IMPORTANT: Note that you'll probably need to "quote" the filename.
     itk::Size classes. The origin of the region within the image with which it
     is associated is defined by Index 
 \end{itemize}
+\item \begin{verbatim}&bands=r1,r2,...,rn\end{verbatim}
+\begin{itemize}
+    \item Select a subset of bands from the output image
+    \item The syntax is inspired by Python indexing syntax with
+      bands=r1,r2,r3,...,rn  where each ri is a band range that can be :
+      \begin{itemize}
+      \item a single index (1-based) :
+        \begin{itemize}
+          \item $'2'$ means 2nd band
+          \item $'-1'$ means last band
+          \end{itemize}
+        \item or a range of bands :
+          \begin{itemize}
+            \item $'3:'$ means 3rd band until the last one
+            \item $':-2'$ means the first bands until the second to last
+            \item $'2:4'$ means bands 2,3 and 4
+          \end{itemize}
+      \end{itemize}
+    \item empty by default (all bands are write from the output image)
+\end{itemize}
 
 \end{itemize}