Add Contribute section to readme.md

Author: wooorm

readme.md

@@ -43,6 +43,14 @@ multiple IDs are found.
 
 [`Node`][hast].
 
+## Contribute
+
+See [`contribute.md` in `syntax-tree/hast`][contribute] for ways to get
+started.
+
+This organisation has a [Code of Conduct][coc].  By interacting with this
+repository, organisation, or community you agree to abide by its terms.
+
 ## License
 
 [MIT][license] © [Titus Wormer][author]
@@ -64,3 +72,7 @@ multiple IDs are found.
 [author]: http://wooorm.com
 
 [hast]: https://github.com/syntax-tree/hast
+
+[contribute]: https://github.com/syntax-tree/hast/blob/master/contributing.md
+
+[coc]: https://github.com/syntax-tree/hast/blob/master/code-of-conduct.md