Add GitHub support document

.github/SUPPORT.md

@@ -0,0 +1,12 @@
+
+# Gutenberg Project Support
+
+Welcome to WordPress' Gutenberg project! We hope you join us in creating the future platform for publishing; all are welcome here.
+
+* Please see the [Contributing Guidelines](https://github.com/WordPress/gutenberg/blob/master/CONTRIBUTING.md) for additional information on how to contribute.
+
+* As with all WordPress projects, we want to ensure a welcoming environment for everyone. With that in mind, all contributors are expected to follow our [Code of Conduct](https://github.com/WordPress/gutenberg/blob/master/CODE_OF_CONDUCT.md).
+
+* Join us on Slack for real-time communication, it is where maintainers coordinate around the project. To get started using Slack, see: https://make.wordpress.org/chat/
+
+* For WordPress support see the [WordPress.org support forums](https://wordpress.org/support/) — it is highly active and well maintained.