Provide general work instructions for HiWis

[NeuroShepherd]

1. Overview of our communication channels
2. Direct them back to GitHub training sections
3. Have them complete (most) of our tutorials if they're not already familiar with the topics
4. Timekeeping and flexibility with work hours--they can use the Excel sheet I created
5. ...

[MalikaIhle]

@muchassgracia this issue is relevant for your current task of compiling all our SOPs and onboarding doc into one structured manual section (in here: https://lmu-osc.github.io/manual/)