Add Gym compatibility blog (#50)

docs/content/gym_compatibility.md

@@ -0,0 +1,30 @@
+---
+layout: "contents"
+title: Compatibility With Gym
+---
+
+# Compatibility with Gym
+Gymnasium provides a number of compatibility methods for a range of Environment implementations. 
+
+## Loading OpenAI Gym environments
+For environments that are registered solely in OpenAI Gym, it is still possible to import environments within Gymnasium.
+Introduced in Gymnasium v0.26.3, in `gymnasium.make`, if the environment id doesn't exist in the 
+gymnasium registry then a check if done to see if the environment is registered in Gym. 
+If it is, then we will make environment using the gym's registration information. 
+
+An example of this is atari 0.8.0 which does not have a gymnasium implementation currently. 
+```python
+import gymnasium as gym
+env = gym.make("ALE/Pong-v5")
+```
+
+## < v0.22 Environment Compatibility
+A number of environments have not updated to the recent Gym changes, in particular since v0.21. 
+Therefore, to increase backward compatibility, Gym and Gymnasium v0.26+ include an `apply_api_compatibility`
+in `{eval-rst}:py:meth:gymnasium.make` parameter that applies a wrappers to convert v0.21 environment to the v0.26 API.
+
+## Step API Compatibility 
+If environments implement the (old) done step API, Gymnasium provides both functions 
+(`{eval-rst}:py:meth:gymnasium.utils.step_api_compatibility.convert_to_terminated_truncated_step_api`) and 
+wrappers (`{eval-rst}:py:meth:gymnasium.wrappers.StepAPICompatibility`) that will convert the 
+step function to the (new) termination and truncation step API. 

docs/index.md

@@ -33,6 +33,7 @@ env.close()
 :caption: Introduction
 
 content/basic_usage
+content/gym_compatibility
 ```
 
 ```{toctree}