Infra: Review existing yarn installs

[ryan-roemer]

We have some legacy yarn installs for logically separate projects in victory. Let's go through and see if we can / should convert them to PNPM:

$ find . -name "yarn.lock" ! -path "*/node_modules/*"
./demo/rn/yarn.lock
./docs/yarn.lock

• [ ] docs
• [ ] RN demo
  • [ ] Also update Victory Native's developer readme: https://github.com/FormidableLabs/victory/tree/main/packages/victory-native#local-development-and-demo and maybe consider just moving to a dedicated section in our root CONTRIBUTING.md