Improve branch naming documentation format in CONTRIBUTING.md

[lessuselesss]

Is your feature request related to a problem? Please describe.

In the CONTRIBUTING.md file, there's some formatting issues in the branch naming section, :

Incorrect nested list numbering (using "1." twice)
Inconsistent formatting for the example (using "eg." instead of "Example:")

This inconsistency with our documentation style could lead to confusion and doesn't match the professional tone of the rest of the document.

Describe the solution you'd like

1. Use proper sequential numbering (1, 2)
2. Replace "eg." with "Example:" to match documentation style
3. Use a more clear example number (9999)

The final format should look like:

3. Fork the repo and create your branch from `main`.
    
    1. The name of the branch should start with the issue number and be descriptive of the changes you are making.  
    2. Example: 9999--add-test-for-bug-123]

Describe alternatives you've considered

1. Keeping "eg." but it's less formal than our documentation style
2. Using different formatting like "For example:" or "(example:)" but "Example:" is cleaner
3. Using a bullet point for the example, but numbered lists better show the relationship between the instruction and its example

Additional context

This change aligns with our documentation styleguide and makes the contribution guidelines more consistent and professional. It's a small change that improves readability and maintains our documentation standards.

[ileana-pr]

Fixed: #1191