Added instructions on how to Install neovim on linux

[bryanvaz]

The instructions on the neovim website don't get you to the same point where the video starts (as my unfortunate afternoon found out).

These instructions fill in the gap for a how to get a clean, mainline Linux distro to the point where the video starts.

TODO: Figure out how to get there for a mac because otherwise they're all stuck on VSCode

[Sefriol]

OSX installation is pretty simple.
Terminal etc configurations are typically under ~/.config/.

# Install nvim using brew
brew install neovim
# Move to config directory
cd ~/.config/
# Create nvim directory
mkdir nvim
# Start Neovim in file explorer mode
nvim .

For OSX other things are also required. To get the ps-grep command working brew install ripgrep needs to be installed.