Update CONTRIBUTING.md to emphasize the importance of meaningful commit messages

### Overview

We want the `CONTRIBUTING.md` file to emphasize that devs need to write clear and descriptive messages when making commits.

### Action Items

- [ ] Add instructions reminding developers to write clear, descriptive commit messages.

In section **2.7.c Working on an issue(3): Prepare your changes to push to your repository**, after the sentence:

> To commit your changes with a message, run:
```bash
git commit -m “insert message here”
```

Please add the following sentence:

_Your commit message should be clear, concise, and descriptive about what changes are being made._

### Resources/Instructions

**📌 Why this matters**

Developers may assume that commit messages don’t matter, since the squash and merge strategy typically replaces them with the PR title. However, this isn’t guaranteed. When there’s only one commit, the original commit message is used. Regardless of the merge method, writing clear and meaningful commit messages is a good practice.