Update D0 generation code for selecting specific decay channel

Update D0 generation code for selecting D0->pi+K decay channel. Also decayed pion and kaon are required to be within ePIC acceptance of |eta| < 3.5

pythia8.306-1.0

What's Changed

• Update README.md by @rahmans1 in #1
• Create main41_D0.cc by @rahmans1 in #2

New Contributors

• @rahmans1 made their first contribution in #1

Full Changelog: https://github.com/eic/D0Gen/commits/pythia8.306-1.0