Update uuid4 VO readme.

#17

Author: n1nj4t4nuk1

README.md

@@ -15,6 +15,7 @@ A collection of Value Objects to save time by generalizing types and format vali
   * [String value-objects](#string-value-objects)
     * [String](#string)
     * [Nullable String](#nullable-string)
+    * [Uuid4](#uuid4)
 
 
 # Value-objects
@@ -83,4 +84,16 @@ my_nullable_str = NullableString(None)
 
 # Getting raw value
 my_nullable_str.value() # returns -> None
+```
+
+### Uuid4
+
+```python
+from pyvalueobjects import Uuid4
+
+# Creation
+my_uuid4 = Uuid4('6c7add12-bf35-459e-a6c5-3178a2a33011')
+
+# Getting raw value
+my_uuid4.value()  # returns -> '6c7add12-bf35-459e-a6c5-3178a2a33011'
 ```