make a single place to set version number and provide a README.md with build instructions

[fduncanh]

I managed to build nvidia-settings for 525.116.04 which you don't
provide a version for (running on openSUSE with nvidia drivers
from URL: https://download.nvidia.com/opensuse/leap/15.5
which don't include the nvidia-settings utility).

The nvidia version is hardcoded in a number of places. It would be better
to set it once in the top level src directory.

A readme file would be helpful for build instructions
(An open SUSE quirk was that their wayland include
files are in /usr/include/wayland, not /usr/include)

If there was any encouragement to do so, I could make a PR request for these changes

[aaronp24]

The code here is generated from an internal repository that gets its version number from a single location. This repository is just a mirror of the output of that.

You shouldn't need to change the version number in order to use nvidia-settings with 525.116.04 anyway. It's intended to provide a reasonable range of compatibility across driver versions, although there have been some incompatibilities in the past. Can you use the 535.43.02 build of nvidia-settings with the 525.116.04 driver?