Add link to the README concerning make options/targets

Author: ksuess

docs/contributing/core/index.md

@@ -96,7 +96,7 @@ Install Plone and run it:
 make run
 ```
 
-See more `make` options/targets in the READMEs of the `buildout.coredev` repo.
+See more `make` options/targets in the READMEs of the `buildout.coredev` repo: https://github.com/plone/buildout.coredev/blob/6.1/README-make.md
 
 
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