[SDXL, Docs] Textual inversion (#5039)
* [SDXL, Docs] Textual inversion
* Update docs/source/en/using-diffusers/sdxl.md
* finish
* Apply suggestions from code review
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>
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Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>
