[manual] suggested addition to hsv doc

[John W. Eaton]

On 19-Sep-2008, Francesco Potorti` wrote:

|  -- Function File:  hsv (N)
|      Create color colormap. This colormap is red through yellow, green,
|      cyan, blue, magenta to red.
| 
| I suggest adding the following:
| 
| It is obtained by linearly varying the hue through all possible values
| while keeping constant maximum saturation and value.
| Equivalent to hsv2rgb([linspace(0,1,N)' ones(N,2)]).

I made this change.

Thanks,

jwe