Update README.md

Author: dmgcodevil

hystrix-contrib/hystrix-javanica/README.md

@@ -326,7 +326,32 @@ Based on [this](https://github.com/Netflix/Hystrix/wiki/How-To-Use#ErrorPropagat
     }
 ```
 
-If `userResource.getUserById(id);` throws an exception which type is _BadRequestException_ then this exception will be thrown without triggering fallback logic.
+If `userResource.getUserById(id);` throws an exception that type is _BadRequestException_ then this exception will be wrapped in ``HystrixBadRequestException`` and re-thrown without triggering fallback logic. You don't need to do it manually, javanica will do it for you under the hood. It is worth noting that a caller will get root cause exception, i.e. user ``BadRequestException``. A caller always gets root cause exception, never ``HystrixBadRequestException`` or ``HystrixRuntimeException`` except the case when executed code explicitly throws those exceptions. 
+
+*Note*: If command has a fallback then only first exception that trigers fallback logic will be propagated to caller. Example:
+
+```java
+class Service {
+    @HystrixCommand(fallbackMethod = "fallback")
+    Object command(Object o) throws CommandException {
+        throw new CommandException();
+    }
+    
+    @HystrixCommand
+    Object fallback(Object o) throws FallbackException {
+        throw new FallbackException();
+    }
+}
+
+// in client code
+{
+    try {
+        service.command(null);
+    } catch (Exception e) {
+      assert CommandException.class.equals(e.getClass())
+    }
+}
+```
 
 ## Request Cache
 
@@ -531,6 +556,24 @@ ThreadPoolProperties can be set using @HystrixCommand's 'threadPoolProperties' l
     }
 ```
 
+### DefaultProperties
+``@DefaultProperties`` is class (type) level annotation that allows to default commands properties such as ``groupKey``, ``threadPoolKey``, ``commandProperties``, ``threadPoolProperties`` and ``ignoreExceptions``. Properties specified using this annotation will be used by default for each hystrix command defined within annotated class unless a command specifies those properties explicitly using corresponding ``@HystrixCommand`` parameters. 
+Example:
+
+```java
+@DefaultProperties(groupKey = "DefaultGroupKey")
+class Service {
+    @HystrixCommand // hystrix command group key is 'DefaultGroupKey'
+    public Object commandInheritsDefaultProperties() {
+        return null;
+    }
+    @HystrixCommand(groupKey = "SpecificGroupKey") // command overrides default group key
+    public Object commandOverridesGroupKey() {
+        return null;
+    }
+}
+```
+
 ## Hystrix collapser
 
 Suppose you have some command which calls should be collapsed in one backend call. For this goal you can use ```@HystrixCollapser``` annotation.