chore: adds contributor guidelines

Author: kbknapp

CONTRIBUTING.md

@@ -0,0 +1,28 @@
+# How to Contribute
+
+Contributions are always welcome! Please use the following guidelines when contributing to `cargo-graph`
+
+1. Fork `cargo-graph`
+2. Clone your fork (`git clone https://github.com/$YOUR_USERNAME/cargo-graph && cd cargo-graph`)
+3. Create new branch (`git checkout -b new-branch`)
+4. Make your changes, and commit (`git commit -am "your message"`)
+ * I use a [conventional](https://github.com/ajoslin/conventional-changelog/blob/a5505865ff3dd710cf757f50530e73ef0ca641da/conventions/angular.md) changelog format so I can update my changelog using [clog](https://github.com/clog-tool/clog-cli)
+ * In addition to the conventions defined above, I also use `imp`, `wip`, `examples`.
+ * Format your commit subject line using the following format: `TYPE(COMPONENT): MESSAGE` where `TYPE` is one of the following:
+    - `feat` - A new feature
+    - `imp` - An improvement to an existing feature
+    - `perf` - A performance improvement
+    - `docs` - Changes to documentation only
+    - `tests` - Changes to the testing framework or tests only
+    - `fix` - A bug fix
+    - `refactor` - Code functionality doesn't change, but underlying structure may
+    - `style` - Stylistic changes only, no functionality changes
+    - `wip` - A work in progress commit (Should typically be `git rebase`'ed away)
+    - `chore` - Catch all or things that have to do with the build system, etc
+    - `examples` - Changes to existing example, or a new example
+ * The `COMPONENT` is optional, and may be a single file, directory, or logical component. Can be omitted if commit applies globally
+5. Run the tests (`cargo test `)
+6. `git rebase` into concise commits and remove `--fixup`s (`git rebase -i HEAD~NUM` where `NUM` is number of commits back)
+7. Push your changes back to your fork (`git push origin $your-branch`)
+8. Create a pull request! (You can also create the pull request first, and we'll merge when ready. This a good way to discuss proposed changes.)
+