Various QoL and documentation improvements

[tomodachi94]

• Use Markdown headings on the README.md file.
• Add links to CurseForge from the README.md.
• Add issue templates, which will make bugs and feature requests easier to comprehend, as well as automatically tagging them as such.
• Add a CI workflow for the project with GitHub Actions, to ensure builds succeed when they are pushed.
• Add a .gitignore, to ignore junk and temporary files when committing.