Update README for setup on non-Unreal projects and add error check

[LilithSilver]

This PR updates the README file with instructions for building/including in a non-Unreal C++ project (it's currently a bit of a pain and took me a while to figure out). It also updates the example and provides some troubleshooting steps.

I also included an error check in the STL file read ifstream mode to ensure the file was opened properly. It earlier failed on the parsing step and produced an endianness error; it now properly reports the error to the user. I included this because it also tripped me up for a bit.

The test file passes when I run it with -C Release, but not -C Debug (standing issue, not caused by my changes).

Let me know if I should change or add anything!

[JBenda]

Thanks for updating the readme . The additional error check is a good idea :+1
But could you add the name of the file to the error message, this might be usefull if the user generates its filenames.

[LilithSilver]

But could you add the name of the file to the error message, this might be usefull if the user generates its filenames.

Pushed!