The content of the following wiki pages is documented in https://github.com/RIOT-OS/RIOT/blob/master/CONTRIBUTING.md:

• https://github.com/RIOT-OS/RIOT/wiki/Contributing-to-RIOT
• https://github.com/RIOT-OS/RIOT/wiki/Guidelines%20for%20Creating%20a%20Good%20Pull%20Request

I suggest to remove the wiki pages to reduce redundancy and improve maintainability.
In case CONTRIBUTING.md lacks content, we should move content from the wiki pages to this file.