Merge pull request #139 from sbt/fix-proxy-repo-instructions

Update 04-Proxy-Repositories.md

src/reference/02-DetailTopics/03-Dependency-Management/04-Proxy-Repositories.md

@@ -70,6 +70,8 @@ be able to resolve sbt plugins.
 The final resolver is `my-maven-proxy-releases`. This repository is a
 proxy for all standard maven repositories, including maven central.
 
+This repositories file is all that's required to use a proxy repository.  These repositories will get included first in any sbt build, however you can add some addtiionaly configuration to force the use of the proxy repository instead of other configurations.
+
 #### Launcher Script
 
 The sbt launcher supports two configuration options that allow the usage
@@ -90,6 +92,8 @@ It is specified like so:
 -Dsbt.override.build.repos=true
 ```
 
+The value defaults to false and must be explicitly enabled.
+
 #### `sbt.repository.config`
 
 If you are unable to create a `~/.sbt/repositories` file, due to user