Added project roadmap to readme (#377)

README.md

@@ -15,6 +15,7 @@ The documentation website is at [minigrid.farama.org](https://minigrid.farama.or
 
 Note that the library was previously known as gym-minigrid and it has been referenced in several publications. If your publication uses the Minigrid library and you wish for it to be included in the [list of publications](https://minigrid.farama.org/content/publications/), please create an issue in the [GitHub repository](https://github.com/Farama-Foundation/Minigrid/issues/new/choose).
 
+See the [Project Roadmap](https://github.com/Farama-Foundation/Minigrid/issues/363) for details regarding the long-term plans.
 
 # Installation