docs: renamed CONTRIBUTING.md to CODE_OF_CONDUCT.md and fixed link

Author: bbrauneck

CONTRIBUTING.md renamed to CODE_OF_CONDUCT.md

@@ -13,7 +13,7 @@
 
 various commands
 
-[![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)](code_of_conduct.md)
+[![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)](CODE_OF_CONDUCT.md)
 
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