Add explicit information about task dplot

doc/user/dplot.tex

@@ -14,7 +14,7 @@ from SCF or DFT calculation. The output file is either in
 (default)
  or in the 
 \htmladdnormallink{Gaussian Cube}{http://www.gaussian.com/00000430.htm}  
-format. 
+format.  DPLOT is not executed until the "task dplot" directive is given.  
 Different sub-directives are described below.
 
 \section{GAUSSIAN --- Gaussian Cube format}