docs(forms): add package overview for forms (#25663)

PR Close #25663

packages/forms/PACKAGE.md

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+Implements a set of directives and providers to communicate with native DOM elements when building forms 
+to capture user input. 
+
+Use this API to register directives, build form and data models, and provide validation to your forms. Validators can
+be synchronous or asynchronous depending on your use case. You can also extend the built-in functionality
+provided by forms in Angular by using the interfaces and tokens to create custom validators and input elements.
+
+Angular forms allow you to:
+
+* Capture the current value and validation status of a form.
+* Track and listen for changes to the form's data model.
+* Validate the correctness of user input.
+* Create custom validators and input elements.
+
+You can build forms in one of two ways:
+
+* *Reactive forms* use existing instances of a `FormControl` or `FormGroup` to build a form model. This form
+model is synced with form input elements through directives to track and communicate changes back to the form model. Changes
+to the value and status of the controls are provided as observables.
+* *Template-driven* use directives such as `NgModel` and `NgModelGroup` that provide two-way data binding to 
+track changes within the template using the change detection cycle.
+
+
+@see Find out more in the [Forms Overview](guide/forms-overview).