docs: Minor changes to Contributing.md

[Grazerquart]

• Changed URL in the clone command to make it clearer that you should be cloning forked branch
• Bolded Section titles for readability

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud