* Remove duplicated instructions
* Move Vim's 8 instructions to the top and add more detailed steps
* Update INSTALL.md (from review)
* update install instructions for plugin managers
And reformat some markdown
Co-authored-by: D. Ben Knoble <ben.knoble@gmail.com>
Co-authored-by: D. Ben Knoble <ben.knoble+github@gmail.com>