Add plugin directory submission form link to README (#238)

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README.md

@@ -25,7 +25,7 @@ Internal plugins are developed by Anthropic team members. See `/plugins/example-
 
 ### External Plugins
 
-Third-party partners can submit plugins for inclusion in the marketplace. External plugins must meet quality and security standards for approval.
+Third-party partners can submit plugins for inclusion in the marketplace. External plugins must meet quality and security standards for approval. To submit a new plugin, use the [plugin directory submission form](https://clau.de/plugin-directory-submission).
 
 ## Plugin Structure