doc: update readme with usage

packages/wyatt_form_bloc/README.md

@@ -30,21 +30,25 @@ Form Bloc for Dart & Flutter.
 ## Features
 
 - Form
-    * FormInput: *atom of a form*
+    * FormInputValidator:
         - Store data
         - Validate this data
-    * FormEntry: *shell of this atom*
+    * FormInputMetadata:
+        - Store infos and options about an input.
+    * FormEntry:
         - Associate a key to an input
         - Configure form attribute (exportation, name...)
-    * FormData: *collection of entries*
+    * FormInput:
-        - Contain all entries
+        - Associaite a key, to a validator and metadata.
+    * FormData: *collection of inputs*
+        - Contain all inputs
         - Basic set operation
 
 - FormDataCubit
     * Data management behind a form.
         - Use entries to pass a FormData object
-        - You can use several pre configured FormInput for validation
+        - You can use several pre configured `FormInputValidator` for validation
-        - You can use updateFormData() to change FormData and validators during runtime (intersection, union, difference or replace)
+        - You can use updateFormData() to change `FormData` during runtime (intersection, union, difference or replace)
 
 - Consistent
     * Every class have same naming convention
@@ -59,4 +63,120 @@ import 'package:wyatt_form_bloc/wyatt_form_bloc.dart';
 
 ## Usage
 
-todo
+Firstly, you have to create your form inputs.
+
+```dart
+static List<FormInput> getNormalEntries() {
+    return const [
+        FormInput(formFieldName, Name.pure()),
+        FormInput(formFieldEmail, Email.pure()),
+        FormInput(formFieldPhone, Phone.pure()),
+        FormInput(formFieldList, ListOption<String>.pure(defaultValue: ['checkbox3'])),
+        FormInput(formFieldRadio, TextString.pure()),
+        FormInput(formFieldPro, Boolean.pure(), metadata: FormInputMetadata<void>(name: 'business')),
+        FormInput(formFieldHidden, Boolean.pure(), metadata: FormInputMetadata<void>(export: false)),
+    ];
+}
+
+static List<FormInput> getBusinessEntries() {
+    const entries = [
+        FormInput(formFieldSiren, Siren.pure()),
+        FormInput(formFieldIban, Iban.pure()),
+    ];
+    return getNormalEntries() + entries;
+}
+
+static FormData getNormalFormData() {
+    return FormData(getNormalEntries());
+}
+
+static FormData getProFormData() {
+    return FormData(getBusinessEntries());
+}
+```
+
+> Let's create functions to enable dynamic changes in runtime.
+
+> When creating metadata with `FormInputMetadata<T>`, `T` is the type of `extra` object.
+
+Then a `FormData` is a collection of inputs. You can `validate`, `contains`, `intersection`, `difference`, `union`, or `clone` this data.
+
+After that, you have to extends `FormDataCubit`.
+
+```dart
+class CustomFormCubit extends FormDataCubit {
+  CustomFormCubit({required FormData inputs}) : super(inputs: inputs);
+
+  @override
+  Future<void> submitForm() {
+    log(state.data.toMap().toString());
+    // Handle all your logic here.
+    emit(...)
+  }
+}
+```
+
+> The submited form is in `state.data` !
+
+Don't forget to create and provide it !
+
+```dart
+FormDataCubit _formCubit = CustomFormCubit(inputs: getNormalFormData());
+
+return BlocProvider(
+    create: (context) => _formCubit,
+    child: const WidgetTree(),
+);
+```
+
+You can now create the first form input !
+
+```dart
+class _EmailInput extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return BlocBuilder<FormDataCubit, FormDataState>(
+      builder: (context, state) {
+        return TextField(
+          onChanged: (email) => context
+              .read<FormDataCubit>()
+              .dataChanged(formFieldEmail, Email.dirty(email)),
+          keyboardType: TextInputType.emailAddress,
+          decoration: InputDecoration(
+            labelText: 'email',
+            helperText: '',
+            errorText: state.data.isNotValid(formFieldEmail)
+                ? 'invalid email'
+                : null,
+          ),
+        );
+      },
+    );
+  }
+}
+```
+
+Then, you can create the trigger
+
+```dart
+class _SignUpButton extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return BlocBuilder<FormDataCubit, FormDataState>(
+      buildWhen: (previous, current) => previous.status != current.status,
+      builder: (context, state) {
+        return state.status.isSubmissionInProgress
+            ? const CircularProgressIndicator()
+            : ElevatedButton(
+                onPressed: state.status.isValidated
+                    ? () => context.read<FormDataCubit>().submitForm()
+                    : null,
+                child: const Text('SIGN UP'),
+              );
+      },
+    );
+  }
+}
+```
+
+> With `state.status` you can access the status of the form to check if there is an error or if it's in submission.