Add the fact that the CHANGELOG.md needs to be modified to reflect changes in CONTRIBUTING.md

[realraphrous]

This issue is just to propose a small change that may not necessarily be relevant.

As of today, it does not seem obvious / clear that CHANGELOG.md should be modified after a change: #4818 #4794 and #4810 (after Jak's suggestions on Discord). Currently, the contribution process is describe in CONTRIBUTING.md as follows:

• Find or open a GitHub issue relevant to the change you wish to make and comment saying that you wish to work on this issue. If the change introduces new functionality or behaviour this would be a good time to discuss the details of the change to ensure we are in agreement as to how the new functionality should work.
• Open a GitHub pull request with your changes and ensure the tests and build pass on CI.
• A Gleam team member will review the changes and may provide feedback to work on. Depending on the change there may be multiple rounds of feedback.
• Once the changes have been approved the code will be rebased into the main branch.

It would be interesting to add an extra line to the process to indicate that our changes should be reflected in the CHANGELOG.md file, such as:

• Reflect your changes in CHANGELOG.md under Unreleased (h2) at the top of the file. Find the best section (h3) to describe your changes. You can draw inspiration from the changes made previously.

(Not exactly sure for the wording)

In itself, this is not the most significant change. After some discussions with Gleam team members, the contributor will understand what needs to be modified. Above all, this clarifies who is responsible for modifying this file.

[giacomocavalieri]

That's a great idea! I'm all for it

[GearsDatapacks]

Sounds good!
As to the wording, you probably don't need h2 and h3 in there, that's only important when adding the headings. In most cases they will already be present

[realraphrous]

Gonna do that tonight !