add installation instructions for vim-plug & Plug (#248)

* add installation instructions for vim-plug & Plug

* Add call plug#begin() and plug#end()

* Removing the comments

Removing the comment inside setup to avoid confusion

README.md

@@ -4,9 +4,34 @@ A super powerful autopair plugin for Neovim that supports multiple characters.
 
 Requires neovim 0.5+
 
-### Setup
-``` lua
-require('nvim-autopairs').setup{}
+## Installation
+
+Install the plugin with your preferred package manager:
+
+### [vim-plug](https://github.com/junegunn/vim-plug)
+
+```vim
+" Vim Script
+call plug#begin()
+" other plugins
+Plug 'windwp/nvim-autopairs'
+call plug#end()
+
+lua << EOF
+require("nvim-autopairs").setup {}
+EOF
+```
+
+### [packer](https://github.com/wbthomason/packer.nvim)
+
+```lua
+-- Lua
+use {
+	"windwp/nvim-autopairs",
+		config = function()
+			require("nvim-autopairs").setup {}
+	end
+}
 ```
 
 ## Default values