Add Instructions for adding external environments (#1210)

docs/environments/third_party_environments.md

@@ -25,17 +25,25 @@ goal-RL ([Gymnasium-Robotics](https://robotics.farama.org/)).
 ## Third-party environments with Gymnasium
 *This page contains environments which are not maintained by Farama Foundation and, as such, cannot be guaranteed to function as intended.*
 
-*If you'd like to contribute an environment, please reach out on [Discord](https://discord.gg/MHCFauP67z), then submit a PR by editing this [file](https://github.com/Farama-Foundation/Gymnasium/blob/main/docs/environments/third_party_environments.md).*
+*If you'd like to contribute an environment, please reach out on [Discord](https://discord.gg/MHCFauP67z), then submit a PR by editing this [file](https://github.com/Farama-Foundation/Gymnasium/blob/main/docs/environments/third_party_environments.md), additional instructions can be found inside that file*
 
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+  A short 2-5 sentence description.
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+<!-- Instructions
+- Follow the template in the file
+- Environments and environment categories are alphabetically sorted
+- You are responsible for picking the environment category, if you would like to add a category please ask
+- Name your PR something like "Add external environment X"
+-->
+
+
 
 ### Autonomous Driving environments
 *Autonomous Vehicle and traffic management.*