Here's a Clover guide.
Set your BIOS to AHCI/Legacy/Optimus Enabled
Use the attached files as bootpack, goes into /EFI/Clover after you have install Clover according to the guide / Legacy Mode
Note: The Nvidia is not supported and will be disabled with my attached files. So external connection is not supported either since they are hardwired to the Nvidia card.
E6520_Disabled-NVS_HS.zip