Add file detailing some general rules for contribution to the project

This change adds a new file, CONTRIBUTING.md, that details some
generally applicable rules for the contribution to this project. It also
links this file from the README.

nitrocli/README.md

@@ -101,6 +101,13 @@ It is recommended that the resulting executable be installed in a
 directory accessible via the `PATH` environment variable.
 
 
+Contributing
+------------
+
+Contributions are generally welcome. Please follow the guidelines
+outlined in [CONTRIBUTING.md](doc/CONTRIBUTING.md).
+
+
 Acknowledgments
 ---------------
 

nitrocli/doc/CONTRIBUTING.md

@@ -0,0 +1,23 @@
+The following rules generally apply for pull requests and code changes:
+
+**Submit Pull Requests to the `devel` branch**
+
+The `devel` branch is where experimental features reside. After some
+soak time they may be ported over to `master` and a release will be cut
+that includes them.
+
+**Keep documentation up-to-date**
+
+Please make an effort to keep the documentation up-to-date to the extent
+possible and necessary for the change at hand. That includes adjusting
+the [README](../README.md) and [`man` page](nitrocli.1) as well as
+regenerating the PDF rendered version of the latter by running `make
+doc`.
+
+**Blend with existing patterns and style**
+
+To keep the code as consistent as possible, please try not to diverge
+from the existing style used in a file. Specifically for Rust source
+code, use [`rustfmt`](https://github.com/rust-lang/rustfmt) and
+[`clippy`](https://github.com/rust-lang/rust-clippy) to achieve a
+minimum level of consistency and prevent known bugs, respectively.