How do I set up the Programmer Dvorak key layout on Mac OSX El Capitan?
// , The following worked, in my case, for setting up the Programmer Dvorak key layout on Mac OSX "El Capitan": 

Adding Programmer Dvorak to the list of available layouts


These steps must be performed from a user account with administrator access. By default, the main user of the computer has this capability.
Open Safari and download the layout driver package. Safari will put this file into the ~/Downloads folder, unpack it and then start the installer.
If you are on Mavericks (or later), you must hold down the Control key while you click the package icon, and then confirm to Gatekeeper that you want to open the package.
Choose Continue to skip the introduction screen of the package installer.
Make sure that your main harddisk is selected as the target of the installation, and then click the Continue button.
Click on the Install button to start installation.
Enter your password to make a system modification, and then click on the OK button.
Click on the Close button to acknowledge a successful installation.
Alternatively you can do an automated, non-interactive installation of the layout using this command:  

sudo installer -pkg "~/Downloads/Programmer Dvorak v1.2.pkg" -target /



10. In El Capitan, you must now clear the layout cache before new layouts are recognized:  

sudo rm -f /System/Library/Caches/com.apple.IntlDataCache.le*



THEN restart your computer, check your list of available keyboard layouts, and clear the cache again. After another restart, your new keyboard layout should be available.  


Setting up your account to use the Programmer Dvorak layout in El Capitan


Click on the Apple menu in the upper, left corner of the screen.
Choose System Preferences... from the menu that appears.
Click on the Keyboard icon in the second row in the window that
opens.
Select the Input Sources header.
Click the + button in the lower, left corner.
Select the English language at the top of the list on the left side.
Select the Programmer Dvorak layout at the top of the list on the
right side.
Click the Add button in the lower, right corner.
Tick the Show Input menu in menubar checkbox at the bottom of the
window.
Close the Keyboard window.
Click on the Input Menu icon (the little keyboard or flag) in the
upper-right corner of the screen.
Select Programmer Dvorak from the list that is displayed.