Update docs/quick-start.md: add headers inside the install section

These headers should make it perfectly clear that there are two steps to be done to install with the playbook

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

docs/quick-start.md

@@ -94,8 +94,12 @@ Before editing those two files, make sure to read explanations on them to unders
 
 After editing `vars.yml` and `hosts` files, let's start the **installation** procedure.
 
+### Update Ansible roles
+
 Before installing, you need to update the Ansible roles in this playbook. To update them, run `just roles` on your local computer.
 
+### Run installation command
+
 Then, run the command below to start installation:
 
 ````sh