fix code of conduct text

Author: campoy

engineering/documentation.md

@@ -255,7 +255,7 @@ inside `.github/CODE_OF_CONDUCT` for each repository.
 ```markdown
 # Code of Conduct
 
-All activities source{d} projects are governed by the [source{d} code of conduct](https://github.com/src-d/guide/blob/master/.github/CODE_OF_CONDUCT.md).
+All activities under source{d} projects are governed by the [source{d} code of conduct](https://github.com/src-d/guide/blob/master/.github/CODE_OF_CONDUCT.md).
 ```
 
 TL;DR: