Uncomment example client

Keep the example, but prevent errors due to
missing league/oauth2-facebook package.

knpuniversity/oauth2-client-bundle/1.20/config/packages/knpu_oauth2_client.yaml

@@ -1,15 +1,16 @@
 knpu_oauth2_client:
     # configure your clients as described here: https://github.com/knpuniversity/oauth2-client-bundle#configuration
     clients:
-        # will create a service: "knpu.oauth2.client.facebook_main"
-        facebook_main:
-            # this will be one of the supported types
-            type: facebook
-            client_id: '%env(FB_ID)%'
-            client_secret: '%env(FB_SECRET)%'
-            # the route that you're redirected to after
-            # see the controller example below
-            redirect_route: connect_facebook_check
-            # route parameters to pass to your route, if needed
-            redirect_params: {}
-            graph_api_version: v2.12
+        # # will create a service: "knpu.oauth2.client.facebook_main"
+        # first, run `composer require league/oauth2-facebook`
+        # facebook_main:
+        #     # this will be one of the supported types
+        #     type: facebook
+        #     client_id: '%env(FB_ID)%'
+        #     client_secret: '%env(FB_SECRET)%'
+        #     # the route that you're redirected to after
+        #     # see the controller example below
+        #     redirect_route: connect_facebook_check
+        #     # route parameters to pass to your route, if needed
+        #     redirect_params: {}
+        #     graph_api_version: v2.12