docs: 更新README并添加文件上传mock配置

- 移除文件上传相关文档（已从代码中移除）
   - 新增未来计划：动态参数、HTTPS、可视化管理界面
   - 添加 upload.yaml mock 配置文件

mocks/v1/upload.yaml

@@ -0,0 +1,23 @@
+id: "upload_file"
+request:
+  method: "POST"
+  path: "/api/v1/upload"
+  headers:
+    Content-Type: "multipart/form-data"
+response:
+  status: 200
+  headers:
+    Content-Type: "application/json"
+  body: >
+    {
+      "code": 0,
+      "data": {
+        "filename": "example.txt",
+        "path": "storage/2024-01-15/example.txt",
+        "size": 1024,
+        "url": "/storage/2024-01-15/example.txt"
+      },
+      "msg": "upload success"
+    }
+settings:
+  delay_ms: 100