docs: action condition configuration (#73)

docs/configuration.md

@@ -8,8 +8,9 @@
 4. [Location configuration](#location-configuration)
 5. [`GameObject` configuration](#gameobject-configuration)
 6. [Action configuration](#action-configuration)
-7. [Example of full configuration structure](#example-of-full-configuration-structure)
-8. [Example configurations](#example-configurations)
+7. [Condition configuration](#condition-configuration)
+8. [Example of full configuration structure](#example-of-full-configuration-structure)
+9. [Example configurations](#example-configurations)
 
 ## Root directory
 
@@ -177,7 +178,9 @@ common part first. Each action consists of following properties
 
 * `tag` - Action tag; this is required however it is not used for now. Action tag does not have to be unique for now.
 * `type` - One of action types mentioned above.
-* *(optional)* `before` - Configuration of action to be triggered before the proper action is executed,
+* *(optional)* `condition` - Condition configuration. The action won't be executed until the condition is satisfied.
+    Aliases: `requires`. See [condition configuration](#condition-configuration)
+* *(optional)* `before` - Configuration of action to be triggered before the proper action is executed.
   e.g. you may want to change location before starting the dialogue. (TODO: Logic is not implemented as for now).
 * *(optional)* `after` - Configuration of action to be triggered after the proper action is executed, e.g. you may want
     give player some output or item. (TODO: Logic is not implemented as for now).
@@ -212,6 +215,15 @@ Let's look at specific action types:
   * `assetPath` - Path to the image with background for the dialogue window. As any path, it must be eiter absolute or relative to the engine's source root.
     Aliases: `asset-path`, `asset`.
 
+## Condition configuration
+
+Describes condition that must be satisfied before the action can be executed.
+
+Condition consists of following properties:
+
+* `type` - One of types:
+  * `item-required` - Requires following props:
+    * `item-tag` - Tag of the item that must be in the player inventory for the action to be executed.
 
 ## Example of full configuration structure