Improve docs

Author: smowton

java/ql/src/semmle/code/java/dataflow/internal/DataFlowForSerializability.qll

@@ -1,10 +1,19 @@
 /**
  * Provides classes for performing local (intra-procedural) and
- * global (inter-procedural) data flow analyses.
+ * global (inter-procedural) data flow analyses (for internal use only).
+ *
+ * This copy of the library is exclusively for use by `Serializability.qll` and
+ * related libraries. Configurations computed using this instance of the library
+ * are in scope whenever `java.qll` is imported, and are used to compute among
+ * other things `AdditionalTaintStep`.
  */
 
 import java
 
+/**
+ * Provides classes for performing local (intra-procedural) and
+ * global (inter-procedural) data flow analyses (for internal use only).
+ */
 module DataFlowForSerializability {
   import semmle.code.java.dataflow.internal.DataFlowImplForSerializability
 }