Getter example

[matthewmueller]

It wasn't immediately obvious how to actually loop over this array from the examples. Something like this would be helpful to newcomers:

var mat = ndarray([1, 2, 3, 4, 5, 6, 7, 8, 9], [3,3])
var m = mat.hi(2, 2)

console.log('at: %s', m.get(2, 2));
for(var i=0; i < m.shape[0]; ++i) {
  for(var j=0; j < m.shape[1]; ++j) {
    console.log('(%s, %s): %s', i, j + m.offset, mat.get(i, j + m.offset));
  }
}

I can open a PR to add it to the Readme, if you're interested, or if there's a better way to improve this, so it's more generic.

[mikolalysenko]

Looks good to me! If you want to write something I will merge it in.