Installing kali linux not bootable on mac

I have a big problem trying to install kali linux on an external hard drive. Everything works good untill the part where i have to boot from that hard... I.m using a macbook pro early 2011 and i just cant see that hard in boot screen.

I saw some articles telling me i have to install "rEFInd" first, but i have 2 hard drives in my laptop 1 with mac on it, another one with windows 8.1. If i install rEFInd the hard with windows will boot just normal or there will be complications or something?

Is there an easyer way to install kali linux on an external hard drive and being able to get it around me and use it on any computer without needed to install additional stuff on that computer ?

(i have a bootable stick but is working only on windows computers not on mac too)

Thank you.