Update screenshot for enabling accessibility for Yosemite/El Capitan?

[dxclancy]

http://mizage.com/help/accessibility.html#10.10

[dxclancy]

Above url is a page that shows where to go on each OS version for accessibility. might be good to add to readme

Here is a new screenshot from Yosemite you can use if you wish: (not sure if same in El Capitan)