fix ollama create's usage string

[todashuta]

Since StringP() automatically adds the initial value, the initial value description for Modelfile was duplicated.
I have fixed this by removing the redundant default value description from the usage.

Before:

$ ./ollama create -h
Create a model from a Modelfile

Usage:
  ollama create MODEL [flags]

Flags:
  -f, --file string       Name of the Modelfile (default "Modelfile") (default "Modelfile")
  -h, --help              help for create
  -q, --quantize string   Quantize model to this level (e.g. q4_0)

Environment Variables:
      OLLAMA_HOST        The host:port or base URL of the Ollama server (e.g. http://localhost:11434)

After:

$ ./ollama create -h
Create a model from a Modelfile

Usage:
  ollama create MODEL [flags]

Flags:
  -f, --file string       Name of the Modelfile (default "Modelfile")
  -h, --help              help for create
  -q, --quantize string   Quantize model to this level (e.g. q4_0)

Environment Variables:
      OLLAMA_HOST        The host:port or base URL of the Ollama server (e.g. http://localhost:11434)

[jmorganca]

Thanks!