Add doc pages for notable Atari environment sets

docs/environment-sets.md

@@ -0,0 +1,20 @@
+---
+firstpage:
+lastpage:
+---
+
+# Environment Sets
+
+Research papers rarely benchmark on all of the games the ALE supports, several well-known subsets are used instead.
+The pages below list the games belonging to each notable set:
+
+- [Complete list](environments/complete_list) — all 104 games supported by the ALE.
+- [Atari 57](environments/atari_57) — the 57 games used by DeepMind to benchmark agents, from DQN through Agent57.
+- [Previously in OpenAI Gym](environments/gym) — the 62 games that were registered in OpenAI Gym.
+
+```{toctree}
+:hidden:
+environments/complete_list
+environments/atari_57
+environments/gym
+```

docs/environments.md

@@ -117,6 +117,15 @@ environments/zaxxon
    :file: environments/list.html
 ```
 
+## Environment sets
+
+Research papers rarely benchmark on all of the games the ALE supports, several well-known subsets are used instead.
+The pages below list the games belonging to each notable set:
+
+- [Complete list](environments/complete_list) — all 104 games supported by the ALE.
+- [Atari 57](environments/atari_57) — the 57 games used by DeepMind to benchmark agents, from DQN through Agent57.
+- [Previously in OpenAI Gym](environments/gym) — the 62 games that were registered in OpenAI Gym.
+
 ## Action Space
 
 Each environment will use a sub-set of the full action space listed below: