Update README.md

adding in a contribution section from the removal of the contributing.md file

Author: parispittman

README.md

@@ -251,3 +251,24 @@ been merged into `main`.
 
 If you are interested in developing `swift-format`, there is additional
 documentation about that [here](Documentation/Development.md).
+
+## Contributing
+
+Contributions to Swift are welcomed and encouraged! Please see the
+[Contributing to Swift guide](https://swift.org/contributing/).
+
+Before submitting the pull request, please make sure you have [tested your
+ changes](https://github.com/apple/swift/blob/main/docs/ContinuousIntegration.md)
+ and that they follow the Swift project [guidelines for contributing
+ code](https://swift.org/contributing/#contributing-code).
+
+To be a truly great community, [Swift.org](https://swift.org/) needs to welcome
+developers from all walks of life, with different backgrounds, and with a wide
+range of experience. A diverse and friendly community will have more great
+ideas, more unique perspectives, and produce more great code. We will work
+diligently to make the Swift community welcoming to everyone.
+
+To give clarity of what is expected of our members, Swift has adopted the
+code of conduct defined by the Contributor Covenant. This document is used
+across many open source communities, and we think it articulates our values
+well. For more, see the [Code of Conduct](https://swift.org/code-of-conduct/).