I want to flash the gapps package onto a custom storage disk. It is unbranded. It has Android 5.1 arm but no google apps (no google play, google play services, etc). I don't wish to root my phone. I have the gapps package (.zip file) for Android 5.1 arm installed.
I have looked into Heimdall (I have a mac and linux devices) but they both look like they are for Samsung devices, or maybe even Nexus ones. I've not found a single reliable tool that can flash the package on an unbranded storage disk. I would also like to know how I can get TWRP or CWM on this storage disk.
If I could get a whole step-by-step process of what to do, I will be extremely grateful.
tl;dr- I would like to know a step-by-step process of how to flash gapps onto a custom, unbranded storage disk. Please include details about which flashing software to use and how to get TWRP or CWM on this disk.
IMPORTANT: Please take into consideration that only mac and linux devices are accessible to me.