Step 1: After downloading the file above, plug your PS Vita into USB using VitaShell or use MolecularShell to start an FTP Client. If you dont know how to do that follow my video on the HENKaku exploit here
Step 2: Navigate to the directory ux0:/ on your Vita, if using VitaShell your already there and place the realboy.vpk here.
Step 3: Now navigate to the ux0:/data folder on your Vita and create a folder called "realboy" so it should look like this "ux0:/data/realboy" place your gameboy roms in here.
Step 4: Once you've done that exit your FTP client or your VitaShell USB connection and navigate on your Vita to the ux0:/ root and find the realboy.vpk file and press X to install and the X again to confirm and your done.
Now just simply go to your XMB and load up real boy and you'll already be loaded to the ux0:/ root and just navigate to "ux0:/data/realboy" and press X to load whatever ROM you have.