docs: fix nvidia-container-runtime usage example

[iacker]

This updates the nvidia-container-runtime usage example so it follows the runtime path described earlier in the README: the NVIDIA runtime modifies the OCI spec when a create command is detected, then the container can be started.

The old example used run, which skips the modifier path and leaves the generated config.json unchanged, as reported in #781.

Fixes #781

Validation:

• Confirmed the old nvidia-container-runtime run nvidia_smi example is no longer present.
• Confirmed the replacement example uses create, start, and cleanup with delete.

AI assistance disclosure:

• I used AI assistance to identify the stale example and prepare this small documentation update.

[copy-pr-bot]

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