Add guide to build for Linux, need cmake, make and copy data folder

[brozkeff]

I tried to manually build the plugin on Linux (Ubuntu 22.04 but with OBS 30.2.3 from PPA) using cmake & make. It succesfully built obs-doom-transition.so file which I moved to ~/.config/obs-studio/plugins/obs-doom-transition/bin/64bit/ folder. However the .so file crashes OBS with SIGSEGV as it fails with Could not find doom_transition.effect when trying to use it.

Once the data folder is copied to ~/.config/obs-studio/plugins/obs-doom-transition/data/ everything works on Linux - both transition effects. (Version 1.3.0)

Consider building the Linux version properly or supplying with the guide how to do it:

# How to build on Linux (Ubuntu/Debian/Mint):

git clone https://github.com/LucienHH/obs-doom-transition/
cd obs-doom-transition
# install required packages, at least:
sudo apt-get install cmake build-essential
mkdir build
cd build
cmake ..
make

# and then create ~/.config/obs-studio/plugins/obs-doom-transition folder
# and copy freshly built obs-doom-transition.so to bin/64bit/ subfolder
# and then the entire data/ folder from the git repo to ~/.config/obs-studio/plugins/obs-doom-transition/data

Screenshot of working plugin on Ubuntu:

[LucienHH]

Thanks for looking into building with Linux, when putting this together I didn't have time to build and test for platforms other than Windows but do plan on adding those builds. Will keep this issue open to track this work.