Update Readme.md

It seems that type is not in the scope bindings of this directive. 

So I updated the examples, since they are not working.

Or you can change the directive to add it to the bindings. That is your choice what you prefer ...

Also I would prefer that 
if ($scope.chart) { type = $scope.chart; }
should be extended that type has a fallback value, like line chart. So that the code will not crash if type is not set.