Add CONTRIBUTING.md

CONTRIBUTING.md

@@ -0,0 +1,15 @@
+# Contributing to `sealed`
+
+- Ensure you're using Rust 1.56.0 to develop and test.
+  This is required because we test macro error messages, which are not stable across
+  compiler versions. Pinning the version everyone uses when developing `sealed` was the
+  solution I found. If you know of a better solution,
+  [let me know](https://github.com/jmg-duarte/sealed-rs/issues/new)!
+
+- If you're adding new functionality, add tests to the new functionality and existing
+  ones, ensuring they all play nice with each other!
+
+- If you're fixing existing functionality, start by adding a minimal reproducible
+  example as a test and fix the code until you achieve the desired behavior.
+
+Have fun!

README.md

@@ -50,6 +50,9 @@ This is the list of arguments that can be used in a `#[sealed]` attribute:
 
 - `#[sealed(pub(crate))]` or `#[sealed(pub(in some::path))]`: allows to tune visibility of the generated sealing module (the default one is private). This useful when the trait and its impls are defined in different modules. For an example, see [`nesting`](examples/nesting.rs) example. **Notice**, that just `pub` is disallowed as breaks the whole idea of sealing.
 
+### Contributing
+
+See [CONTRIBUTING.md](CONTRIBUTING.md).
 
 #### License