docs: clarify reference image brush behavior in description

app.py

@@ -762,13 +762,14 @@ def build_app():
     _DESCRIPTION_EN = """\
 **RefineAnything** refines local regions of an image guided by a text prompt. \
 Upload a source image, **brush over the area** you want to edit, and describe the desired change. \
-Optionally upload a second reference image for style/content guidance.\
+Optionally upload a reference image for style/content guidance — \
+leave it as-is to reference the whole image, or **brush on it** to specify exactly which region to reference.\
 """
 
     _DESCRIPTION_CN = """\
 **RefineAnything** 根据文字提示精修图片的局部区域。\
 上传一张源图，**用画笔涂抹**需要编辑的区域，再输入想要的修改描述即可。\
-可选上传第二张参考图来引导风格/内容。\
+可选上传第二张参考图来引导风格/内容——不涂抹则参考整张图，**涂抹则精确指定参考区域**。\
 """
 
     with gr.Blocks(title="RefineAnything", theme=gr.themes.Soft()) as demo: