docs: update README clone URL

[thehanslevi]

Summary

• update the README clone command to use this repository's current URL
• update the following cd command to match the checkout directory from that URL

Validation

• cloned the public repository successfully after sandbox DNS retry
• verified the old and current clone URLs both resolve to the same HEAD
• verified the current URL basename is Deep-Reinforcement-Learning-Algorithms-with-PyTorch
• rg -n 'Deep_RL_Implementations|Deep-Reinforcement-Learning-Algorithms-with-PyTorch|git clone|cd Deep' README.md
• git diff --check

This is a README-only change for issue #73.