convert : clarify sentence-transformers-dense-modules help [no ci] (#18662)

convert : clarify sentence-transformers-dense-modules help [no ci] (#18662)

* convert : clarify sentence-transformers-dense-modules help [no ci]

This commit updates this options help message which currently looks
like this:
```console
  --sentence-transformers-dense-modules
                        Whether to include sentence-transformers dense modules.It can be used for sentence-transformers models, like
                        google/embeddinggemma-300mDefault these modules are not included.
```