Hardcoded Path in src/CMakeLists.txt

[lesharris]

There is a hardcoded path in src/CMakeLists.txt that prevents building the project on a system without that directory structure:

	pico_generate_pio_header(sig_gen /home/pi/Documents/pico/paulsProjects/sig_gen/manchester_encoding.pio)

A simple update to fix this is to use CMAKE_CURRENT_LIST_DIR instead:

	pico_generate_pio_header(sig_gen ${CMAKE_CURRENT_LIST_DIR}/manchester_encoding.pio)

I can open a PR if you would prefer but it is a quick edit. Also, thank you very much for this project!

[wasspaul]

Thanks for your correction. I will fix it on my build system, verify it works for me and update GitHub (I will also fix some typos in the read me).