docs: add README

README.md

@@ -1,6 +1,62 @@
 Field Guard
 ===========
 
+[Middleware](https://github.com/x-graphql/field-middleware) for adding security layer to GraphQL schema
+
+![unit tests](https://github.com/x-graphql/field-guard/actions/workflows/unit_tests.yml/badge.svg)
+[![codecov](https://codecov.io/gh/x-graphql/field-guard/graph/badge.svg?token=a76EAc7BUy)](https://codecov.io/gh/x-graphql/field-guard)
+
+Getting Started
+---------------
+
+Install this package via [Composer](https://getcomposer.org)
+
+```shell
+composer require x-graphql/field-guard
+```
+
+Usages
+------
+
+Create permissions array mapping object type name, and it fields with rule, rule can be
+boolean or instance of `XGraphQL\FieldGuard\RuleInterface`:
+
+```php
+use GraphQL\Type\Definition\ResolveInfo;
+use XGraphQL\FieldGuard\RuleInterface;
+
+$isAdminRule = new class implements RuleInterface {
+    public function allows(mixed $value, array $args, mixed $context, ResolveInfo $info) : bool{
+        return $context->isAdmin();
+    }
+
+    public function shouldRemember(mixed $value,array $args,mixed $context,ResolveInfo $info) : bool{
+        return true;
+    }
+};
+
+$permissions = [
+    'Query' => [
+        'getUser' => true, /// all user can get user.
+        'getBook' => false, /// deny all user to get book.
+    ],
+    'Mutation' => [
+        'createUser' => $isAdminRule, /// only admin user can create user.
+    ]   
+];
+```
+
+Then create middleware with `$permissions` above and apply to schema:
+
+```php
+use XGraphQL\FieldMiddleware\FieldMiddleware;
+use XGraphQL\FieldGuard\FieldGuardMiddleware;
+
+$schema = ...
+$guardMiddleware = new FieldGuardMiddleware($schema, $permissions);
+
+FieldMiddleware::apply($schema, [$guardMiddleware]);
+```
 
 Credits
 -------