Add example usage to documentation, minor bugfixes to environments

[elliottower]

Description

• Added sections Installation and Usage sections in each md file to make it more obvious how to use each of them (there have been a few questions on discord which this would help with)
• Updated RLcard envs step() functions to call render() if render_mode is set to "human" (consistent with other envs)
• Cleaned up Butterfly manual_policy examples: supply render_mode (fixes warning when running code) and remove unnecessary render() call, and made env initialization be called first to be consistent with all other examples (group pygame and manual control code together as they are the distinct parts to the manual control examples as compared to any other example)
• Add documentation example on Butterfly for running manual_policy example (currently the only way to find this code is by digging through the files and finding the example script, also it's not clear that there even is manual control unless you click on the individual page)
• Cleaned up Butterfly documentation to remove prisoner example which no longer exists (was moved to tutorial)

Type of change

Documentation update

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have run pytest -v and no errors are present.
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I solved any possible warnings that pytest -v has generated that are related to my code to the best of my knowledge.
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[elliottower]

Doing pytest -v the leduc holdem test currently fails but when I remove my changes (adding a simple render() call to the step function) the fail still occurs. Will look into the cause of it and try to fix it though. All other tests seem to pass.

[jjshoots]

Overall a very good PR. I wonder why no one else has caught the render in step catch before (myself included), and the documentation improvements are definitely much needed. There's just one minor comment --- but I presume that's to match the gymnasium way of doing things.

[jjshoots]

Why is there a need for this change?

[elliottower]

Yep it was just for consistency, drove me crazy having to remember if it’s tests or testing but other repos use testing