add days 1-4

[alv67]

📑 Description

Closes #

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

ℹ Additional Information

[gmacario]

As a personal preference and to minimize issues when checking out the repository from different OSs, I would tend to use lowercase characters for the directories, i.e. solutions/$USER/day01 rather than solutions/$USER/Day01

Apart from that, LGTM. Merging PR

[gmacario]

See above