Add explantion on how to override config settings with env vars

README.md

@@ -9,6 +9,12 @@ ARC is a transaction processor for Bitcoin that keeps track of the life cycle of
 Settings for ARC are defined in a configuration file. The default configuration file is `config.yaml` in the root directory. Each setting is documented in the file itself.
 If you want to load `config.yaml` from a different location, you can specify it on the command line using the `-config=<path>` flag.
 
+Each setting in the file `config.yaml` can be overridden with an environment variable. The environment variable needs to have this prefix `ARC_`. A sub setting will be separated using an underscore character. For example the following config setting could be overridden by the environment variable `ARC_METAMORPH_LISTENADDR`
+```yaml
+metamorph:
+  listenAddr:
+```
+
 ## Microservices
 
 To run all the microservices in one process (during development), use the `main.go` file in the root directory.
@@ -37,7 +43,7 @@ where options are:
 
     -tracer=<true|false>
           whether to start the Jaeger tracer (default=false)
-  
+
     -config=<path>
           path to config file (default='')
 ```