Merge pull request #2 from pamil/docs

Finish "Usage" section in readme

Author: pamil

README.md

@@ -13,6 +13,7 @@ Allows to declare and use contexts services in scenario scoped container.
 2. Enable and configure context service extension in your Behat configuration:
 
     ```yaml
+    # behat.yml
     default:
         # ...
         extensions:
@@ -22,3 +23,50 @@ Allows to declare and use contexts services in scenario scoped container.
                    - "features/bootstrap/config/services.yml"
                    - "features/bootstrap/config/services.php"   
     ```
+    
+3. Inside one of those files passed to configuration above, create a service tagged with `fob.context_service`.
+
+    ```xml
+    <!-- features/bootstrap/config/services.xml -->
+    <?xml version="1.0" encoding="UTF-8" ?>
+    <container xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://symfony.com/schema/dic/services">
+        <services>
+            <service id="acme.my_context" class="Acme\MyContext">
+                <tag name="fob.context_service" />
+            </service>
+        </services>
+    </container>
+    ```
+    
+    ```yaml
+    # features/bootstrap/config/services.yml
+    services:
+        acme.my_context:
+            class: Acme\MyContext
+            tags:
+                - { name: fob.context_service }
+    ```
+    
+    ```php
+    // features/bootstrap/config/services.php
+ 
+    use Symfony\Component\DependencyInjection\Definition;
+    
+    $definition = new Definition(\Acme\MyContext::class);
+    $definition->addTag('fob.context_service');
+    $container->setDefinition('acme.my_context', $definition);
+    ```
+
+4. Configure your suite to use `acme.my_context` context service (note **contexts_services** key instead of **contexts**):
+
+    ```yaml
+    # behat.yml
+    default:
+        # ...
+           suites:
+               default:
+                   contexts_services:
+                       - acme.my_context
+    ```
+
+5. Have fun with your contexts defined in DI container as services! :tada: