Fixed broken link for Contributing doc

I included the link to the contributing doc file

content/README.md

@@ -4,7 +4,7 @@ The `/content` directory is where all the site's (English) Markdown content live
 
 See the [markup reference guide](contributing/content-markup-reference.md) for more information about supported Markdown features.
 
-See the [contributing docs](contributing) for general information about working with the docs.
+See the [contributing docs](https://github.com/github/docs/blob/main/CONTRIBUTING.md) for general information about working with the docs.
 
 - [Frontmatter](#frontmatter)
   - [`versions`](#versions)