Move vim-plug installation outside of config.

It is a one-time thing. Do not waste precious time checking it every
time we start Nvim.

docs/README.md

@@ -156,6 +156,38 @@ Make sure that you can call `nvim` from the command line after all these setups.
 
 # Setting up Nvim
 
+## Install plugin manager vim-plug
+
+I use [vim-plug](https://github.com/junegunn/vim-plug) to manage all my
+plugins. We need to install vim-plug on our system first.
+
+For Windows, if curl is installed, use the following command:
+
+```
+curl -fLo ~\AppData\Local\nvim-data\site\autoload\plug.vim --create-dirs https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim
+```
+
+Or execute the following command on PowerShell:
+
+```
+md ~\AppData\Local\nvim-data\site\autoload
+$uri = 'https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim'
+(New-Object Net.WebClient).DownloadFile(
+  $uri,
+  $ExecutionContext.SessionState.Path.GetUnresolvedProviderPathFromPSPath(
+    "~\AppData\Local\nvim-data\site\autoload\plug.vim"
+  )
+)
+```
+
+Or just create the directory `~\AppData\Local\nvim-data\site\autoload\`, and put the vim-plug script there.
+
+For macOS and Linux, use the following command:
+
+```bash
+curl -fLo ~/.local/share/nvim/site/autoload/plug.vim --create-dirs https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim
+```
+
 ## How to install this configuration
 
 On Windows, the config directory is `$HOME/AppData/Local/nvim`[^1]. On Linux
@@ -167,12 +199,11 @@ command to install this configuration:
 git clone https://github.com/jdhao/nvim-config.git .
 ```
 
-After that, when we first open nvim, all the plugins included in this
+After that, when we first open nvim, use `:PlugInstall` to install all the
-configuration will be installed automatically for you (for Windows and macOS).
+plugins. Since I use quite a lot of plugins (more than 60), it may take some
-Since I use quite a lot of plugins (around 60 plugins), it may take some time
+time to install all of them, depending on your network condition.
-to install all of them, depending on your network condition.
 
-# Automatic Installation #
+# Automatic Installation for Linux #
 
 To set up a workable Neovim environment in Linux, I use the script
 [`Nvim_setup.sh`](Nvim_setup.sh) to automatically install necessary

plugins.vim

@@ -1,30 +1,15 @@
 scriptencoding utf-8
 "{ Plugin installation
-"{{ Vim-plug Install and related settings
+"{{ Vim-plug related settings.
+" The root directory to install all plugins.
+let g:PLUGIN_HOME=expand(stdpath('data') . '/plugged')
 
-" Auto-install vim-plug on different systems if it does not exist. For
+if empty(readdir(g:PLUGIN_HOME))
-" Windows, only Windows 10 with curl installed are supported (after Windows 10
+ augroup plug_init
-" build 17063, source:
+    autocmd!
-" https://devblogs.microsoft.com/commandline/tar-and-curl-come-to-windows/).
+    autocmd VimEnter * PlugInstall --sync | quit |source $MYVIMRC
-" The following script to install vim-plug is adapted from vim-plug
-" wiki: https://github.com/junegunn/vim-plug/wiki/tips#tips
-let g:vim_plug_fpath = expand(stdpath('data') . '/site/autoload/plug.vim')
-if (g:is_win || g:is_mac) && !filereadable(g:vim_plug_fpath)
-  if !executable('curl')
-    echoerr 'Curl not available on your system, you may install vim-plug by yourself.'
-    finish
-  endif
-  echomsg 'Installing Vim-plug on your system'
-  let g:vim_plug_furl = 'https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim'
-  silent execute printf('!curl -fLo %s --create-dirs %s', g:vim_plug_fpath, g:vim_plug_furl)
-  augroup plug_init
-      autocmd!
-      autocmd VimEnter * PlugInstall --sync | quit |source $MYVIMRC
   augroup END
 endif
-
-" The directory to install plugins.
-let g:PLUGIN_HOME=expand(stdpath('data') . '/plugged')
 "}}
 
 "{{ Autocompletion related plugins