Add more hints for MacOS installation issues

[jlperla]

  ## Some Common Errors on MacOS
  - To open a terminal on MacOS
    - Press `Cmd + Space` to open Spotlight, then type `Terminal`
    - Or with VS Code `<Cmd-Shift-P>` then `View: Toggle Terminal` 
  - If you get permissions problems try
    ```
    sudo curl -fsSL https://install.julialang.org | sh
    ```
  - If it still shows errors, then [see here](https://github.com/JuliaLang/juliaup/wiki/Permission-problems-during-setup) and do some combo of 
    ```
    sudo chown $(id -u):$(id -g) ~/.bashrc
    sudo chown $(id -u):$(id -g) ~/.zshrc
    sudo chown $(id -u):$(id -g) ~/.bash_profile
    ```
    - Then retry `sudo curl -fsSL https://install.julialang.org | sh`