📚 Add onboarding documents for different roles

About
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AIM is a large project and starting on it can be pretty daunting; it would be nice to have onboarding documentation for the various roles within AIM in this repo.

I think it'd be helpful to have documentation specific to the different positions people have - e.g. working for AIM vs. AIM RSF.

To-do
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- [x] figure out how many versions of the onboarding make sense -> always have the boiler plate be the most up to date
- [x] figure out a way to keep the various versions synced but separate (if possible) -> have a boiler plate that gets updated and then archive the new starter files into a folder
- [x] create first drafts
- [ ] get feedback from people in those positions
- [ ] finalise the documents
- [ ] make sure they're easy to find

Stakeholders
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This is relevant for everyone working in AIM/AIM RSF with the primary contacts being EZ and SB.

Activity
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EZ added some drafts to the onboarding branch (https://github.com/aim-rsf/Getting-Started/blob/onboarding-docs/onboarding/rsf-turing-staff.md) . These are based on the documentation that SB created.