Hard-wrap installation instructions for Windows (#649)

Long snippets are sometimes difficult to fully select in a Web browser.
Hard wrapping snippets to make them easier to grab.

README.md

@@ -41,7 +41,12 @@ curl -fLo ~/.vim/autoload/plug.vim --create-dirs \
 ```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"))
+(New-Object Net.WebClient).DownloadFile(
+  $uri,
+  $ExecutionContext.SessionState.Path.GetUnresolvedProviderPathFromPSPath(
+    "~\vimfiles\autoload\plug.vim"
+  )
+)
 ```
 
 #### Neovim
@@ -58,7 +63,12 @@ curl -fLo ~/.local/share/nvim/site/autoload/plug.vim --create-dirs \
 ```powershell
 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("~\AppData\Local\nvim\autoload\plug.vim"))
+(New-Object Net.WebClient).DownloadFile(
+  $uri,
+  $ExecutionContext.SessionState.Path.GetUnresolvedProviderPathFromPSPath(
+    "~\AppData\Local\nvim\autoload\plug.vim"
+  )
+)
 ```
 
 ### Getting Help