jps build: javadocs added

jps/jps-builders/src/org/jetbrains/jps/builders/BuildRootDescriptor.java

@@ -69,6 +69,9 @@ public abstract class BuildRootDescriptor {
     return Collections.emptySet();
   }
 
+  /**
+   * Returns {@code true} if the whole content of this source root was automatically generated by the JPS build process.
+   */
   public boolean isGenerated() {
     return false;
   }

jps/model-api/src/org/jetbrains/jps/model/java/JavaSourceRootProperties.java

@@ -62,6 +62,11 @@ public class JavaSourceRootProperties extends JpsElementBase<JavaSourceRootPrope
     return new JavaSourceRootProperties(myPackagePrefix, myForGeneratedSources);
   }
 
+  /**
+   * Returns {@code true} if the source root contain only sources which were automatically generated by some program. Classes from such
+   * sources roots can be used in the IDE, they will be compiled with the other sources, etc, however IDE will warn users if they try
+   * editing them manually.
+   */
   public boolean isForGeneratedSources() {
     return myForGeneratedSources;
   }