Fixing where contributing file lives, adding link to main readme doc

Author: ToriLindsay

src/CONTRIBUTING.md renamed to CONTRIBUTING.md

@@ -2,6 +2,8 @@
 
 Welcome to the open-source repository for all [Cloudflare Developer Documentation](https://developers.cloudflare.com/).
 
+To learn how to contribute, visit the [contribution page](https://developers.cloudflare.com/style-guide/contributions/) of the Cloudflare Style Guide.
+
 ## License and Legal Notices
 
 Except as otherwise noted, Cloudflare and any contributors grant you a license to the Cloudflare Developer Documentation and other content in this repository under the [Creative Commons Attribution 4.0 International Public License](https://creativecommons.org/licenses/by/4.0/legalcode), see the [LICENSE file](https://github.com/cloudflare/cloudflare-docs/blob/production/LICENSE), and grant you a license to any code in the repository under the [MIT License](https://opensource.org/licenses/MIT), see the [LICENSE-CODE file](https://github.com/cloudflare/cloudflare-docs/blob/production/LICENSE-CODE).