improve --lora-model-dir documentation

[l29ah]

No description provided.

[leejet]

I don’t think this change adds much to understanding. For users who are not familiar with LoRA, they still need to consult the documentation https://github.com/leejet/stable-diffusion.cpp/blob/master/docs/lora.md to understand how it works; and for users who are already familiar with it, this change doesn’t really provide any additional value either.

[l29ah]

The linked file doesn't contain the information this PR adds, instead If not specified, the default is the current working directory. directly contradicts the current behavior and misleads the user when LoRA doesn't work when the option is not present.

[leejet]

“lora tags in prompt are ignored when unset” is not very accurate here.
When lora_model_dir is not set, LoRA tags are actually treated as normal prompt text. This behavior was likely caused by some previous changes and is now inconsistent with the documentation. #1224 should fix that issue and bring the behavior back in line with the docs.

[l29ah]

Great, thanks!