quick-start.md: deprecated URL login -> SSH login

Issue on private GitHub repos: URL login is deprecared, SSH used instead.

When connecting to GitHub by URL, there was an error:
"Support for password authentication was removed on August 13, 2021.
Please see https://docs.github.com/en/get-started/getting-started-with-git/about-remote-repositories#cloning-with-https-urls for information on currently recommended modes of authentication."

assets/chezmoi.io/docs/quick-start.md

@@ -119,7 +119,7 @@ sequenceDiagram
 On a second machine, initialize chezmoi with your dotfiles repo:
 
 ```console
-$ chezmoi init https://github.com/$GITHUB_USERNAME/dotfiles.git
+$ chezmoi init git@github.com:$GITHUB_USERNAME/dotfiles.git
 ```
 
 This will check out the repo and any submodules and optionally create a chezmoi
@@ -178,7 +178,7 @@ sequenceDiagram
 You can install your dotfiles on new machine with a single command:
 
 ```console
-$ chezmoi init --apply https://github.com/$GITHUB_USERNAME/dotfiles.git
+$ chezmoi init --apply git@github.com:$GITHUB_USERNAME/dotfiles.git
 ```
 
 If you use GitHub and your dotfiles repo is called `dotfiles` then this can be