diff --git a/README.md b/README.md
index 0ffd6dd..0962b98 100644
--- a/README.md
+++ b/README.md
@@ -38,6 +38,7 @@ Feel free to create PR with additions or request removal of some domain (with re
 
 Use 
 
-`cat disposable_email_blacklist.conf your_file | sort -f | uniq -i  > new_file`
+`cat disposable_email_blacklist.conf your_file | tr '[:upper:]' '[:lower:]' | sort -f | uniq -i  > new_file.conf`
+`comm -23 new_file.conf whitelist.conf > disposable_email_blacklist.conf`
 
-to add contents of another file in the same format (domains on new line without @).
+to add contents of another file in the same format (domains on new line without @). It also converts uppercase to lowercase, sorts, removes duplicates and removes whitelisted domains.