Improve docs adding "--gym-packages" argument

[turbotimon]

Description

improve doc adding "--gym-packages" argument

source:

rl-baselines3-zoo/rl_zoo3/train.py

Lines 107 to 112 in e06914e

	parser.add_argument(
	"--gym-packages",
	type=str,
	nargs="+",
	default=[],
	help="Additional external Gym environment package modules to import",

Motivation and Context

• I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

• Documentation (update in the documentation)

Checklist:

• I've read the CONTRIBUTION guide (required)
• I have updated the documentation accordingly.

[araffin]

Thanks for the PR, but I guess we should deprecate --gym-packages, see #390 (package:env_id might already be working)

[turbotimon]

package:env_id is the first thing I tried, but unfortunately it does not work yet (v2.3.0)...

ENV_NAME = 'gym_environment:gym_environment/GridWorld-v0' # My custom environment

# Works
from gymnasium import make_vec
env = make_vec(ENV_NAME) 

# ValueError: gym_environment:gym_environment/GridWorld-v0 not found in gym registry ....
import sys
from rl_zoo3.train import train
sys.argv = ["python", "--algo", "ppo", "--env", ENV_NAME]
train() 

(You could try using this template for custom env)