Add some of the content in Discord as special unit content

[osanseviero]

E.g. from #rl-announcements channel, we got this for unit 2

Hey everyone 👋 .

If you want to go deeper into Stable Baselines3 before our next week unit about Deep Q-Learning you can check these cool environments 🚀

• Minigrid environment: puzzle environments where your agent needs to find the way out using keys 🔐 and doors 🚪 : https://github.com/maximecb/gym-minigrid

• Procgen Benchmark: 16 simple-to-use procedurally-generated gym environments (platform, shooters etc). You have an example with Stable-Baselines3 here: https://stable-baselines3.readthedocs.io/en/master/guide/examples.html#sb3-and-procgenenv

• VizDoom: a Doom like environment 🔥 Nicholas Renotte made a very good tutorial on how to train an agent playing it using Stable Baselines-3: https://youtu.be/eBCU-tqLGfQ

[simoninithomas]

Done: https://github.com/huggingface/deep-rl-class/blob/main/unit2/unit2-bonus/readme.md