Clarify agent/sampler address overrides

Author: yurishkuro

README.md

@@ -55,24 +55,24 @@ The code can be re-generated with
 
 ### Updating Agent Host and Port
 
-The default agent host and port is `127.0.0.1:6831`, you can use a different host/port by updating your reporter configuration.
+The default host and port for Jaeger Agent is `127.0.0.1:6831`. When the application and Jaeger Agent are running in different containers on the same host, the application's notion of `localhost`/127.0.0.1 it restriced to its own container, so in this case it's usually necessary to override the Agent's host/port by updating your reporter configuration:
 
 YAML configuration:
 
 ```yml
 repoter:
-  localAgentHostPort: localhost:6831
+  localAgentHostPort: jaeger-agent:6831
 ```
 
 NOTE: It is not recommended to use a remote host for UDP connections.
 
 ### Updating Sampling Server URL
 
-The default sampling collector URL is `http://127.0.0.1:5778`, you can use a different URL by updating the sampler configuration.
+The default sampling collector URL is `http://127.0.0.1:5778`. Similar to UDP address above, you can use a different URL by updating the sampler configuration.
 
 ```yml
 sampler:
-  samplingServerURL: http://jaeger-collector.local:5778
+  samplingServerURL: http://jaeger-agent.local:5778
 ```
 
 ## License