Most of the Free Software Enthusiasts use GNU/LINUX distros on their machines but coming to mobiles not many of them bother much.
I Personally use a basic keypad mobile which served me well. While a Community volunteer Helped me knowing all the flashing process and encouraged me to buy a NEXUS 5 which I bought at 1900 INR on a website.
It is a 32 GB variant with 2Gb of Ram and Qualcomm Snapdragon 800 series processor. But the Battery life is a bit dull(2300 MAh).
Now Coming to the OS it has Android Marshmallow 6.0 officially supported.
The first Thing is to Unlock it, Install a Custom Recovery(TWRP) and choose a custom ROM to flash.
I used adb to connect it to my machine and unlocked the bootloader, then installed TeamWin Recovery Project, using TWRP sideload feature I installed lineage 16.0 which I downloaded from xda forums.
With the help of a friend, I captured the whole process.
Click on the Below Picture to checkout the video.