The phpdotenv dependency is not strictly required. Suggest to install it. (#482)

Author: pfrenssen

composer.json

@@ -8,7 +8,9 @@
         "ext-curl": "*",
         "ext-json": "*",
         "netresearch/jsonmapper": "^3.0|^4.0|^5.0",
-        "monolog/monolog": "^2.0|^3.0",
+        "monolog/monolog": "^2.0|^3.0"
+    },
+    "suggest": {
         "vlucas/phpdotenv": "^5.0|^6.0"
     },
     "require-dev": {