Add README.md updates for polymorphism.

README.md

@@ -17,6 +17,7 @@ The fantastic ORM library for Golang, aims to be developer friendly.
 * Iteration Support via [Rows](#row--rows)
 * Scopes
 * sql.Scanner support
+* Polymorphism
 * Every feature comes with tests
 * Convention Over Configuration
 * Developer Friendly
@@ -507,6 +508,32 @@ db.Model(&user).Association("Languages").Clear()
 // Remove all relations between the user and languages
 ```
 
+### Polymorphism
+
+Supports polymorphic has-many and has-one associations.
+
+```go
+  type Cat struct {
+    Id    int
+    Name  string
+    Toy   Toy `gorm:"polymorphic:Owner;"`
+  }
+
+  type Dog struct {
+    Id   int
+    Name string
+    Toy  Toy `gorm:"polymorphic:Owner;"`
+  }
+
+  type Toy struct {
+    Id        int
+    Name      string
+    OwnerId   int
+    OwnerType int
+  }
+```
+Note: polymorphic belongs-to and many-to-many are explicitly NOT supported, and will throw errors.
+
 ## Advanced Usage
 
 ## FirstOrInit