Need better installation instructions for Windows

[benknoble]

See this QA with a response from @romainl, who also points out a potential issue with our packadd! instructions. (They are necessary because of #138 #139 #140 #142.)

[romainl]

So you managed to drag me into this after all…

You should move your palette variables from autoload/dracula.vim to colors/dracula.vim.

By doing that, you:

• remove the dependency to autoload/dracula.vim from colors/dracula.vim,
• so you don't need to have dracula in &rtp,
• so you don't need packadd! dracula in your vimrc,
• and you don't break the Airline and Lightline themes because the variables are defined long before they are sourced.

[benknoble]

Sorry romainl; if you're not interested, I suppose you can unsubscribe. The airline issue arose when someone installed the colorscheme but did not activate it and attempted to activate the corresponding airline theme.

Do you have a better suggestion to avoid the duplication that doesn't involve the runtimepath? I suppose some <sfile>:h trickery might work.