Changes the expected input of checkpoint in rsl-rl to an absolute path in...

Changes the expected input of checkpoint in rsl-rl to an absolute path in documentation to avoid ambiguity (#3151)

# Description

If the user directly enters model_xxx.pt, an error will be reported. The
user should be guided to enter a path

## Type of change

- This change requires a documentation update

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there
Co-authored-by: ooctipus <zhengyuz@nvidia.com>

docs/source/overview/reinforcement-learning/rl_existing_scripts.rst

@@ -65,7 +65,7 @@ RSL-RL
             # run script for training
             ./isaaclab.sh -p scripts/reinforcement_learning/rsl_rl/train.py --task Isaac-Reach-Franka-v0 --headless
             # run script for playing with 32 environments
-            ./isaaclab.sh -p scripts/reinforcement_learning/rsl_rl/play.py --task Isaac-Reach-Franka-v0 --num_envs 32 --load_run run_folder_name --checkpoint model.pt
+            ./isaaclab.sh -p scripts/reinforcement_learning/rsl_rl/play.py --task Isaac-Reach-Franka-v0 --num_envs 32 --load_run run_folder_name --checkpoint /PATH/TO/model.pt
             # run script for playing a pre-trained checkpoint with 32 environments
             ./isaaclab.sh -p scripts/reinforcement_learning/rsl_rl/play.py --task Isaac-Reach-Franka-v0 --num_envs 32 --use_pretrained_checkpoint
             # run script for recording video of a trained agent (requires installing `ffmpeg`)
@@ -81,7 +81,7 @@ RSL-RL
             :: run script for training
             isaaclab.bat -p scripts\reinforcement_learning\rsl_rl\train.py --task Isaac-Reach-Franka-v0 --headless
             :: run script for playing with 32 environments
-            isaaclab.bat -p scripts\reinforcement_learning\rsl_rl\play.py --task Isaac-Reach-Franka-v0 --num_envs 32 --load_run run_folder_name --checkpoint model.pt
+            isaaclab.bat -p scripts\reinforcement_learning\rsl_rl\play.py --task Isaac-Reach-Franka-v0 --num_envs 32 --load_run run_folder_name --checkpoint /PATH/TO/model.pt
             :: run script for playing a pre-trained checkpoint with 32 environments
             isaaclab.bat -p scripts\reinforcement_learning\rsl_rl\play.py --task Isaac-Reach-Franka-v0 --num_envs 32 --use_pretrained_checkpoint
             :: run script for recording video of a trained agent (requires installing `ffmpeg`)