Update changelog to highlight pdf_forms

Why is this change needed?
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It's a cool feature and worth promoting.

How does it address the issue?
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Highlight that one of the new options allows enabling PDF forms.

Any links to any relevant tickets, articles, or other resources?
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DocRaptor/docraptor-csharp-private#5 (comment)

Did you complete all of the following?
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- Run test suite?
- Add new tests?
- Consider security implications and practices?

Author: jason-o-matic

CHANGELOG.md

@@ -1,6 +1,6 @@
 ### 4.0.0 [July 14, 2023]
 * Update to openapi-gnerator v6.6.0
-* Add new API options
+* Add new API options (including prince_options[pdf_forms] to enable PDF forms)
 
 ### 3.0.0 [November 15, 2022]
 * Switch API host to more secure api.docraptor.com (dropping old TLS)