[INSTALL-2] Quick Start uses SSH clone and includes a redundant submodule command

## Problem

The Quick Start `git clone` command uses an SSH URL, which fails for users without SSH keys configured. Additionally, the `git submodule update` command that follows is redundant because the preceding `git clone --recursive` already fetches submodules.

## Suggested fix

- Replace the SSH clone URL with the HTTPS path (`https://github.com/NVIDIA-NeMo/RL.git`).
- Remove or comment out the `git submodule update` command.