[Benchmarking] Wiki "layers" section updated

[Jeff McKenna]

Yingqi,

Since it is just lakes, I don't think we need a polygon boundary/outline 
in this case (Andrea seems to agree, see his earlier comments below:

 >
 > AREAWATER_MERGE
 > ----------------
 >
 > The file contains water polygons (lakes and such), it's quite sparse
 > and has 368303 polygons over the Texas state.
 > It seems to make a nice replacement for the tiger_tracts dataset,
 > which is nation wide but contains only 4388 polygons in Texas.
 >
 > I suggest we use the areawater data set for the polygon test,
 > using a uniform bluish fill color with no outline?

Yingqi Tang wrote:
> Shall we have a different color for the polygon boundary? Otherwise hard to tell one polygon from another.

-jeff