eclipse#457 address review comments

Signed-off-by: Emily Jiang <emijiang6@googlemail.com>

spec/src/main/asciidoc/configsources.asciidoc

@@ -157,7 +157,10 @@ Alternatively, for the injection style, the following lookup should be used to r
     @ConfigProperty(name="myprj.some.dynamic.timeout", defaultValue="100")
     private javax.inject.Provider<Long> timeout; 
 ----
-
+Whether a `ConfigSource` supports this dynamic behavior or not is dependent on how it's implemented.
+For an instance, the default `ConfigSource` microprofile-config.properties and Environment Variables are not dynamic 
+while System Properties are dynamic by nature. MicroProfile Config Implementation can decide whether 
+a `ConfigSource` can be dyanamic or not.
 === Cleaning up a ConfigSource
 
 If a `ConfigSource` implements the `java.lang.AutoCloseable` interface  then the `close()` method will be called when the underlying `Config` is being released.