Broken CHANGELOG contributing guideline

[khoi]

Context 🕵️‍♀️

XcodeProj/CHANGELOG.md

Line 1 in 912d40c

 🚀 Check out the guidelines [here](https://github.com/xcodeswift/contributors/blob/master/CHANGELOG_GUIDELINES.md) 

The linked CHANGELOG contributing guideline is broken and I couldn't find the file anywhere.

[Pedro Piñera Buendía]

@khoi we can update the link to point to these guidelines