Add PandaDoc (#2331)

README.md

@@ -520,6 +520,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Html2PDF](https://html2pdf.app/) | HTML/URL to PDF | `apiKey` | Yes | Unknown |
 | [Mercury](https://mercury.postlight.com/web-parser/) | Web parser | `apiKey` | Yes | Unknown |
 | [Notion](https://developers.notion.com/docs/getting-started) | Integrate with Notion | `OAuth` | Yes | Unknown |
+| [PandaDoc](https://developers.pandadoc.com) | DocGen and eSignatures API | `apiKey` | Yes | No |
 | [Pocket](https://getpocket.com/developer/) | Bookmarking service | `OAuth` | Yes | Unknown |
 | [PrexView](https://prexview.com) | Data from XML or JSON to PDF, HTML or Image | `apiKey` | Yes | Unknown |
 | [Restpack](https://restpack.io/) | Provides screenshot, HTML to PDF and content extraction APIs | `apiKey` | Yes | Unknown |