Update README.md with update_relationship

Author: SeaBlooms

README.md

@@ -119,6 +119,18 @@ j1.create_relationship(
 
 ```
 
+##### Update a relationship
+
+```python
+j1.update_relationship(
+    relationship_id='<id-of-relationship-to-update>',
+    properties={
+        "<relationship-property-name": "<relationship-property-updated-value",
+    },
+)
+
+```
+
 ##### Delete a relationship
 
 ```python
@@ -596,4 +608,4 @@ j1.list_account_parameters()
 j1.create_update_parameter(name="ParameterName", value="stored_value", secret=False)
 
 
-```
+```