It was easier to just download the "TWRP-Nexus5repack-AO1.img" (from here) and then renamed it to "recovery.img" and copied it to the root of the phone's internal storage (aka. /sdcard/)
1.) Boot up phone normally, make sure that USB Debugging is enabled (in Developer Options), connect phone to computer via USB.
2.) Then in command prompt (on computer in folder with ADB files), ran this:
adb shell su -c 'dd if=/sdcard/recovery.img of=/dev/block/platform/msm_sdcc.1/by-name/recovery' bs=4096; sync; reboot recovery;"
4.) IMPORTANT: Wait 2 minutes after the screen is black, and then press power button.
Hope this helps someone out there.