guide: Add tutorial for setting up email and user name on GitHub and locally in git

[teodutu]

Many first time contributors (particularly students) run into checkpatch errors like this one [1] caused by authorship issues. They are easily fixed by setting the appropriate name and email both locally and on GitHub, but our contributing guidelines [2] don't specify this. They should be updated to contain explanations on how to correctly set this information.

[1] https://github.com/open-education-hub/operating-systems/actions/runs/6590761580/job/17908015178?pr=339#step:3:570
[2] https://github.com/open-education-hub/operating-systems/blob/main/CONTRIBUTING.md

[andreia-oca]

I am happy to work on this - @teodutu

[andreia-oca]

I believe this issue/repository is not currently updated - so, I will remove myself from assignees :D