Clarify the meaning of bootstrap properties in documentation. Fixes spring-projects#206

Author: Ryan Baxter

docs/src/main/asciidoc/spring-cloud-commons.adoc

@@ -28,7 +28,8 @@ the box it is responsible for loading configuration properties from
 the external sources, and also decrypting properties in the local
 external configuration files. The two contexts share an `Environment`
 which is the source of external properties for any Spring
-application. Bootstrap properties are added with high precedence, so
+application. Bootstrap properties (not `bootstrap.properties` but properties
+ that are loaded during the bootstrap phase) are added with high precedence, so
 they cannot be overridden by local configuration, by default.
 
 The bootstrap context uses a different convention for locating