Update Onboarding Deck

### Dependency
- #43
- #5

### Overview

We need to update the onboarding deck to use the new template so that all our materials have the same look and feel for better user experience.

### Action Items

- [ ] Evaluate feasibility of changing the theme from the current deck to the theme in the Communications Guide
- [ ] If feasible, copy in theme and clean up slides
- [ ] If not feasible, create a new deck using the Communications guide template and copy over content
- [ ] Change all links that reference the deck to the new deck link
- [ ] wiki
- [ ] internship channel pin
- [ ] issues

### Resources/Instructions
[Communication Guide](https://docs.google.com/presentation/d/1u_rAQx9wz7_2XT3mL1zAu1mtUXvds8YNlbMb-cxDGTI/edit#slide=id.ge20e9913cf_0_45)
[Onboarding Deck](https://docs.google.com/presentation/d/1w9086NcRYTGQeTjbp6F0F2YDVSSVDkCiPDkCYxuOloE/edit#slide=id.gd0de62c6b7_1_0)