add CONTRIBUTING.md, pre-commit hook

.githooks/pre-commit

@@ -0,0 +1,9 @@
+#!/bin/sh
+# Redirect output to stderr.
+exec 1>&2
+
+# Run clang-format on staged files; abort the commit if any files are changed
+if ! git clang-format ; then
+    echo "linting made changes to source files; aborting commit"
+    exit 1
+fi

CONTRIBUTING.md

@@ -0,0 +1,30 @@
+# Contributing to pret/pokeheartgold
+
+<!--toc:start-->
+- [Code Formatting](#code-formatting)
+<!--toc:end-->
+
+This document provides a synopsis and loose guidelines for how to contribute to this project. It is a work in progress. Maintainers should expand this document.
+
+## Code Formatting
+
+This repository includes an opinionated `clang-format` specification to ensure that we maintain a common code style. For convenience, a pre-commit hook is also provided in `.githooks` which will run `clang-format` against any staged changes prior to executing a commit.
+
+### Requirements
+
+- `clang-format@17` or newer
+
+### Usage
+
+To set up the pre-commit hook:
+
+```sh
+git config --local core.hooksPath .githooks/
+```
+
+To run the formatter on the full source tree:
+
+```bash
+./format.sh
+```
+