Add requirement for "blabel" plugin

requirements.txt

@@ -1,6 +1,7 @@
 wheel>=0.34.2                   # Wheel
 Django==3.0.7                   # Django package
 pillow==7.1.0                   # Image manipulation
+blabel==0.1.3                   # Simple PDF label printing
 djangorestframework==3.10.3     # DRF framework
 django-dbbackup==3.3.0          # Database backup / restore functionality
 django-cors-headers==3.2.0      # CORS headers extension for DRF