docs: providers info after configuration (#27)

Signed-off-by: Tom Carrio <[email protected]>

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## This PR
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- adds section on providers after the configuration section in README

Signed-off-by: Tom Carrio <[email protected]>

README.md

@@ -96,6 +96,10 @@ class MyApp
 }
 ```
 
+### Provides
+
+The OpenFeature project maintains the [open-feature/php-sdk-contrib](https://github.com/open-feature/php-sdk-contrib) repository, which includes contributed providers and hooks. Vendors can also implement and maintain their own providers as well. We update [the PHP docs page](https://docs.openfeature.dev/docs/reference/technologies/server/php) with these vendors as often as possible.
+
 ## Development
 
 ### PHP Versioning