fix: improve add data section (#740)

docs/data-sources/docs-site.mdx

@@ -0,0 +1,11 @@
+---
+title: 'Code Documentation'
+---
+
+### Code documentation
+
+To add any code documentation website as a loader, use the data_type as `docs_site`. Eg:
+
+```python
+app.add("https://docs.embedchain.ai/", data_type="docs_site")
+```