Docu update.

doc/tex/grid.tex

@@ -98,6 +98,7 @@ Predefined grids are available for global regular, gaussian, HEALPix or icosahed
     \texttt{hp<NSIDE>[b][\_<ORDER>]} defines a global HEALPix grid.
     The \texttt{NSIDE} parameter controls the resolution of the pixellization. 
     It is the number of pixels on the side of each of the 12 top-level HEALPix pixels.
+    The total number of grid pixels is \texttt{12*NSIDE*NSIDE}.
     \texttt{NSIDE=1} generates the 12 (H=4, K=3) equal sized top-level HEALPix pixels.
     \texttt{ORDER} sets the index ordering convention of the pixels, available are \texttt{ring} (default) or \texttt{nest} ordering.
     If the parameter \texttt{b}  is set, the grid cell corners are also calculated.