README.md in mass_insert-0.2.2 vs README.md in mass_insert-0.2.3

@@ -42,14 +42,38 @@
 
 User.mass_insert(values)
 ```
 
 
-## Insertion per batches
+### Insertion per batches
 Due you can get a database timeout error you can specify that the insertion will be in batches.
 Just pass the `per_batch` option with the records per batch. Example...
 ```ruby
 User.mass_insert(values, per_batch: 1000)
+```
+
+
+### Handle unique index on MySQL
+Sometimes we want to ignore errors when adding duplicated records. MySQL has
+the ability to do that with `ON DUPLICATE KEY UPDATE`. By using the option
+`handle_duplication` we will ignore the new values by doing:
+```ruby
+User.mass_insert(values, handle_duplication: true)
+```
+
+```sql
+INSERT INTO table (a,b,c) VALUES (1,2,3)
+  ON DUPLICATE KEY UPDATE a=a,b=b,c=c;
+```
+
+[Read more about MySQL ON DUPLICATE KEY UPDATE...](http://dev.mysql.com/doc/refman/5.7/en/insert-on-duplicate.html)
+
+
+## Running tests
+First at all copy `test/database.yml.example` to `test/database.yml` and update username and password
+for every database adapters. Then, run the following to test the gem against all adapters.
+```
+bundle exec rake test:all
 ```
 
 
 ## Contributing
 1. Fork it