Add contributing info to README

Signed-off-by: Thomas A. Christensen II <25492070+MillironX@users.noreply.github.com>

README.md

@@ -128,6 +128,12 @@ julia> cowsay("He mooed we must fight\nEscape or we'll die\nCows gathered around
                 ||     ||
 ```
 
+## Contributing
+
+If you find a bug in Cowsay.jl, please [file an issue]. I will not be accepting
+any requests for new cowfiles in this repo, though.
+
+[file an issue]: https://github.com/MillironX/Cowsay.jl/issues
 [julia repl]: https://docs.julialang.org/en/v1/manual/getting-started/
 [pkg mode]: https://docs.julialang.org/en/v1/stdlib/Pkg/
 [the documentation]: https://millironx.com/Cowsay.jl/stable