Add a Code of Conduct section.

This section holds two things:
- A note that this project is released with a Code of Conduct and that
  you agree to abide its terms by participating.
- A link to a (/an upcoming) wiki entry, which holds (/will hold)
  additional information regarding the Code of Conduct.

Author: june128

CONTRIBUTING.md

@@ -1,5 +1,15 @@
 # Contributing
 
+## Code of Conduct
+
+Please note that this project is released with a [Contributor Code of Conduct](./CODE_OF_CONDUCT.md).
+By participating in this project you agree to abide by its terms.
+
+More information regarding the Code of Conduct can be found in the
+[Code of Conduct wiki entry](https://github.com/algorithm-archivists/algorithm-archive/wiki/Code-of-Conduct).
+
+## How to Contribute
+
 A contribution guide on how to contribute to the Arcane Algorithm Archive (AAA) can be found on this Wiki page: https://github.com/algorithm-archivists/algorithm-archive/wiki/How-to-Contribute
 
 The community member Buttercak3 also created a video series, explaining the contribution process of the AAA.  You can find a playlist with all videos here: https://www.youtube.com/playlist?list=PL5NSPcN6fRq2vwgdb9noJacF945CeBk8x