Document BACKUP_FOLDER and BACKUP_KEEP

.env.example

@@ -17,5 +17,12 @@ UPLOAD_FOLDER=app/static/uploads
 MAX_CONTENT_LENGTH=52428800  # 50MB max file size
 ALLOWED_EXTENSIONS=pdf,png,jpg,jpeg,gif
 
+# Backup Configuration
+# Where backup archives are written. Keep this OUTSIDE app/static/uploads.
+# Docker: point this at a mounted volume, e.g. /data/backups
+BACKUP_FOLDER=backups
+# Archives to retain after a backup started from the admin UI (0 = keep all)
+BACKUP_KEEP=5
+
 # Application Configuration
 SETS_PER_PAGE=20