Add code of conduct

.github/CONTRIBUTING.md

@@ -29,6 +29,10 @@
 
 * Ask any question about how to use ImageSharp in the [ImageSharp Gitter Chat Room](https://gitter.im/ImageSharp/General).
 
+#### Code of Conduct  
+This project has adopted the code of conduct defined by the [Contributor Covenant](https://contributor-covenant.org/) to clarify expected behavior in our community.
+For more information, see the [.NET Foundation Code of Conduct](https://dotnetfoundation.org/code-of-conduct).
+
 And please remember. ImageSharp is the work of a very, very, small number of developers who struggle balancing time to contribute to the project with family time and work commitments. We encourage you to pitch in and help make our vision of simple accessible imageprocessing available to all. Open Source can only exist with your help.
 
 Thanks for reading!

CODE_OF_CONDUCT.md

@@ -0,0 +1,3 @@
+# Code of Conduct  
+This project has adopted the code of conduct defined by the [Contributor Covenant](https://contributor-covenant.org/) to clarify expected behavior in our community.
+For more information, see the [.NET Foundation Code of Conduct](https://dotnetfoundation.org/code-of-conduct).

README.md

@@ -63,6 +63,10 @@ The **ImageSharp** library is made up of multiple packages:
 - Do you have questions? We are happy to help! Please [join our gitter channel](https://gitter.im/ImageSharp/General), or ask them on [stackoverflow](https://stackoverflow.com) using the `ImageSharp` tag. **Do not** open issues for questions!
 - Please read our [Contribution Guide](https://github.com/SixLabors/ImageSharp/blob/master/.github/CONTRIBUTING.md) before opening issues or pull requests!
 
+### Code of Conduct  
+This project has adopted the code of conduct defined by the [Contributor Covenant](https://contributor-covenant.org/) to clarify expected behavior in our community.
+For more information, see the [.NET Foundation Code of Conduct](https://dotnetfoundation.org/code-of-conduct).
+
 ### API 
 
 Our API is designed to be simple to consume. Here's an example of the code required to resize an image using the default Bicubic resampler then turn the colors into their grayscale equivalent using the BT709 standard matrix.