Add NPOI example for Excel and F#

```fsharp
if [|fname;varCol;valCol;startRow;endRow|] 
   |> Seq.forall(fun x -> (x <> "" && x <> null)) then 
            using(new FileStream(fname, FileMode.Open, FileAccess.Read))<| fun fs               ->
            using(new HSSFWorkbook(fs, true))                           <| fun templateWorkbook ->  
            using(templateWorkbook.GetSheet("Sheet1"))                  <| fun sheet            ->
```