Add a link to contributing.md

ref #194 (comment)

Author: harupong

README.asc

@@ -8,7 +8,7 @@ Like the first edition, the second edition of Pro Git is open source under a Cre
 
 A couple of things have changed since open sourcing the first edition. For one, we've moved from Markdown to the amazing Asciidoc format for the text of the book. We've also moved to using O'Reilly's https://atlas.oreilly.com[Atlas platform] for generating continuous builds of the book so all major formats are always available in every language.
 
-We've also moved to keeping the translations in separate repositories rather than subdirectories of the English repository. See the Contributing section for more information.
+We've also moved to keeping the translations in separate repositories rather than subdirectories of the English repository. See link:CONTRIBUTING.md[Contributing document] for more information.
 
 == How To Generate the Book