README.md update

README.md

@@ -10,11 +10,13 @@ It relies to a large degree on packages:
 
 ## Features:
 
+- __helpers__:
+	- [pqt.ErrorConstraint](https://godoc.org/github.com/piotrkowalczuk/pqt#ErrorConstraint) - if possible extracts constraint from [pq.Error](https://godoc.org/github.com/lib/pq#Error) so it's easy to build switch statements using generated constraints.
 - __query builder__:
 	- [pqtgo.Composer](https://godoc.org/github.com/piotrkowalczuk/pqt/pqtgo#Composer) - builder like object that keeps buffer and arguments but also tracks positional parameters.
 	- [pqtgo.CompositionWriter](https://godoc.org/github.com/piotrkowalczuk/pqt/pqtgo#CompositionWriter) - interface used by generator, allows custom structs to be used as a criteria parameter
 	- [pqtgo.WriteCompositionQueryInt64](https://godoc.org/github.com/piotrkowalczuk/pqt/pqtgo#WriteCompositionQueryInt64) - helper function that generate SQL for [qtypes.Int64](https://godoc.org/github.com/piotrkowalczuk/qtypes#Int64) object.
-	  - [pqtgo.WriteCompositionQueryString](https://godoc.org/github.com/piotrkowalczuk/pqt/pqtgo#WriteCompositionQueryString) - helper function that generate SQL for [qtypes.Int64](https://godoc.org/github.com/piotrkowalczuk/qtypes#String) object.
+	- [pqtgo.WriteCompositionQueryString](https://godoc.org/github.com/piotrkowalczuk/pqt/pqtgo#WriteCompositionQueryString) - helper function that generate SQL for [qtypes.Int64](https://godoc.org/github.com/piotrkowalczuk/qtypes#String) object.
 - __array support__ - golang postgres driver do not support arrays natively, pqt comes with help:
 	- [pqt.ArrayInt64](https://godoc.org/github.com/piotrkowalczuk/pqt#ArrayInt64) - wrapper for []int64, it generates regular SQL array
 	- [pqt.ArrayFloat64](https://godoc.org/github.com/piotrkowalczuk/pqt#ArrayFloat64) - wrapper for []float64, it generates regular SQL array