feat: better documentation clarity across cadence-samples to reduce onboarding friction for new developers

[zawadzkidiana]

Summary
Improved documentation clarity across cadence-samples to reduce onboarding friction for new developers.

Find code changes here: https://github.com/zawadzkidiana/cadence-samples/tree/walkthrough/new_samples/hello_world

Changes

Documentation fixes

• Fixed CLI command syntax in walkthrough (workflow list instead of --workflow list)
• Added Docker troubleshooting section to main README for common setup issues

Visual walkthrough

• Added step-by-step screenshots to hello_world README
• Shows expected terminal output and Cadence Web UI at each step

Code clarity

• Simplified signal workflow naming for better discoverability

Testing
Verified walkthrough end-to-end on local environment.

[zawadzkidiana]

Initial PR draft; want to review walkthrough another time to ensure all commands are correct and the setup feels intuitive.

[zawadzkidiana]

Note: Also modified the config.yaml to route into "cadence-samples" project.

config for sample

domain: "default"
domain: "cadence-samples"

[demirkayaender]

Thanks for starting a great new sample series!