doc: mention HTTPS approach in tutorial git clone step (#1471)

* doc: change tutorial git to suggest HTTPS

Since we're instructing the user to create a new repository, it might be a safe bet to assume that they don't have their SSH keys set up. HTTPS might be a better option in this context.

* docs: keep ssh add https

@hongarc said, "How about keep `SSH` and add `HTTPS`." This is one way to do that.

* Update tutorial-setup.md

docs/tutorial-setup.md

@@ -55,7 +55,9 @@ We highly recommend you to install Yarn, an alternative package manager that has
 5. Clone your repository to your local machine:
 
 ```sh
-git clone git@github.com:USERNAME/docusaurus-tutorial.git
+git clone git@github.com:USERNAME/docusaurus-tutorial.git # SSH
+# or
+git clone https://github.com/USERNAME/docusaurus-tutorial.git # HTTPS
 ```
 
 6. `cd` into the repository which you just created.