Cherrypick warning about --user-words not having any effect

Might be available in full release of Tess4

src/ocrmypdf/__main__.py

@@ -490,6 +490,10 @@ def check_options_advanced(options, log):
             "--pdfa-image-compression argument has no effect when "
             "--output-type is not 'pdfa', 'pdfa-1', or 'pdfa-2'"
         )
+    
+    if tesseract.v4() and (options.user_words or options.user_patterns):
+        log.warning(
+            'Tesseract 4.x ignores --user-words, so this has no effect')
 
 
 def check_options_metadata(options, log):