chore: add contributing instructions

README.md

@@ -57,4 +57,13 @@ The content of each member is described in their respective Rust Doc as well as
 
 ## Contributing
 
+Contributions are welcome and accepted as pull requests on [GitHub][GH]. Feel free to use issues to report bugs,
+missing documentation or suggest improvements of the project.
+
+Note that a most of the code possess documentation, including private modules / items / sections. You can generate
+the complete documentation by using the instructions [above](#usage) and passing the option `--document-private-items`
+to `cargo doc`.
+
+[GH]: https://github.com/LIHPC-Computational-Geometry/honeycomb
+
 ## License