Update installation instruction for Neovim on Windows (junegunn#634)

Close junegunn#633

README.md

@@ -27,14 +27,26 @@ A minimalist Vim plugin manager.
 [Download plug.vim](https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim)
 and put it in the "autoload" directory.
 
+#### Vim
+
 ###### Unix
 
 ```sh
 curl -fLo ~/.vim/autoload/plug.vim --create-dirs \
     https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim
 ```
 
-###### Neovim
+###### Windows (PowerShell)
+
+```powershell
+md ~\vimfiles\autoload
+$uri = 'https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim'
+(New-Object Net.WebClient).DownloadFile($uri, $ExecutionContext.SessionState.Path.GetUnresolvedProviderPathFromPSPath("~\vimfiles\autoload\plug.vim"))
+```
+
+#### Neovim
+
+###### Unix
 
 ```sh
 curl -fLo ~/.local/share/nvim/site/autoload/plug.vim --create-dirs \
@@ -44,9 +56,9 @@ curl -fLo ~/.local/share/nvim/site/autoload/plug.vim --create-dirs \
 ###### Windows (PowerShell)
 
 ```powershell
-md ~\vimfiles\autoload
+md ~\AppData\Local\nvim\autoload
 $uri = 'https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim'
-(New-Object Net.WebClient).DownloadFile($uri, $ExecutionContext.SessionState.Path.GetUnresolvedProviderPathFromPSPath("~\vimfiles\autoload\plug.vim"))
+(New-Object Net.WebClient).DownloadFile($uri, $ExecutionContext.SessionState.Path.GetUnresolvedProviderPathFromPSPath("~\AppData\Local\nvim\autoload\plug.vim"))
 ```
 
 ### Getting Help