Added how to use section

README.md

@@ -14,3 +14,30 @@ Install package using composer
 
 ## How to use
 
+This package includes two modules. They can be used together or each on their own.
+- `MaxDepthModule` validates maximum depth of a query.
+- `MaxNodesModule` validates that size of a query does not exceed maximum number of nodes. 
+    - One node is essentially a single value which is to be resolved. 
+    - This module automatically recognises "multiplier" arguments, such as `limit`, which multiply inner number of nodes for that field.
+        - Default multiplier arguments are `['limit', 'first', 'last']`, but can be changed using second constructor argument.
+        - If you wish to disable this feature, set the constructor argument to empty array.
+
+1. Register selected modules to GraPHPinator:
+
+```php
+$depthModule = new \Graphpinator\QueryCost\MaxDepthModule(
+    10, // selected maximum depth
+);
+$nodesModule = new \Graphpinator\QueryCost\MaxNodesModule(
+    10000, // selected number of nodes
+    ['limit'], // optional: multiplier argument names
+);
+$graphpinator = new \Graphpinator\Graphpinator(
+    $schema,
+    $catchExceptions,
+    new \Graphpinator\Module\ModuleSet([$depthModule, $nodesModule /* possibly other modules */]),
+    $logger,
+);
+```
+
+2. You are all set, queries are validated for maximum depth/maximum number of nodes.