Add error log if CONFIG env variable is not set

CHANGELOG.md

 # Changelog
 
+## next
+
+- Add explicit error message on startup if `CONFIG` env variable is not set
+
 ## 0.4.0a5
 
 - Fix `Recommandations` title display

validata_ui/config.py

@@ -48,6 +48,9 @@ if SHIELDS_IO_BASE_URL:
     SHIELDS_IO_BASE_URL = without_trailing_slash(SHIELDS_IO_BASE_URL)
 
 CONFIG_FILE = os.environ.get("CONFIG_FILE") or None
+if not CONFIG_FILE:
+    log.error("CONFIG_FILE environment variable is not set, can't go further")
+
 CONFIG = None
 if CONFIG_FILE:
     CONFIG_FILE = Path(CONFIG_FILE)