Update README.md

Author: matthenning

README.md

@@ -44,6 +44,16 @@ class UserController extends Controller
 
 # Documentation
 
+### New in v1.4
+
+##### Filter by not existing related models
+
+```
+.../model?filter[!relation.type]=value
+```
+
+Will match if there is no model of the relation where type = 'value'
+
 ### New in v1.3
 
 ##### Use base64 encoded values
@@ -107,4 +117,4 @@ Filter for a base64 encoded value
 
 ### Known issues
 
-* Sorting by related fields doesn't work yet.
+* Sorting by related fields doesn't work yet.