Create CONTRIBUTING.md (#385)

* Create CONTRIBUTING.md

* Update CONTRIBUTING.md

CONTRIBUTING.md

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+# Contribution guidelines
+
+First off, thank you for considering contributing to delta.
+
+If your contribution is not straightforward, please first discuss the change you
+wish to make by creating a new issue before making the change.
+
+## Developing
+
+### Set up
+
+This is no different than other Rust projects.
+
+```shell
+git clone https://github.com/dandavison/delta/
+cd delta
+cargo build
+```
+
+### Useful Commands
+
+- Build release version:
+
+  ```shell
+  cargo build --release
+  ```
+
+- Run Clippy:
+
+  ```shell
+  cargo clippy
+  ```
+
+- Run all tests:
+
+  ```shell
+  make test
+  ```
+
+- Check to see if there are code formatting issues
+
+  ```shell
+  cargo fmt -- --check
+  ```
+
+- Format the code in the project
+
+  ```shell
+  cargo fmt
+  ```