add "set(CMAKE_EXPORT_COMPILE_COMMANDS ON)" to CMakeLists.txt

[jordanwhitede]

I'm working with clangd in neovim and I get a bunch of errors until I've added this line to my CMakeLists.txt and built the plugin in order to generate compile_commands.json - if there's a better way to do this then I'm happy to hear it, otherwise it might be worth just adding this line to the CMakeLists.txt file?