Add Symfony Notifier integration

Integrated Symfony Notifier into the project by adding it to `composer.json` and creating a configuration file `notifier.yaml`. Updated `symfony.lock` to include the recipe configuration for Notifier. Minor documentation formatting issues were also fixed in `index.rst`.

symfony.lock

@@ -296,6 +296,18 @@
             "config/packages/monolog.yaml"
         ]
     },
+    "symfony/notifier": {
+        "version": "5.4",
+        "recipe": {
+            "repo": "github.com/symfony/recipes",
+            "branch": "main",
+            "version": "5.0",
+            "ref": "178877daf79d2dbd62129dd03612cb1a2cb407cc"
+        },
+        "files": [
+            "config/packages/notifier.yaml"
+        ]
+    },
     "symfony/phpunit-bridge": {
         "version": "7.1",
         "recipe": {