update description for /document-preprocessing in API reference (#3729)

docs/pipeline_usage/tutorials/ocr_pipelines/doc_preprocessor.en.md

@@ -477,7 +477,7 @@ Additionally, PaddleX offers three other deployment methods, detailed as follows
 <li><b><code>infer</code></b></li>
 </ul>
 <p>Obtain the document image preprocessing results.</p>
-<p><code>POST /doc_preprocessor</code></p>
+<p><code>POST /document-preprocessing</code></p>
 <ul>
 <li>The attributes of the request body are as follows:</li>
 </ul>

docs/pipeline_usage/tutorials/ocr_pipelines/doc_preprocessor.md

@@ -479,7 +479,7 @@ for res in output:
 <li><b><code>infer</code></b></li>
 </ul>
 <p>获取图像文档图像预处理结果。</p>
-<p><code>POST /doc_preprocessor</code></p>
+<p><code>POST /document-preprocessing</code></p>
 <ul>
 <li>请求体的属性如下：</li>
 </ul>