C++: Add to and clarify some taint library QLDoc.

Author: geoffw0

cpp/ql/lib/semmle/code/cpp/ir/dataflow/DefaultTaintTracking.qll

@@ -1,3 +1,8 @@
+/**
+ * An IR taint tracking library that uses an IR DataFlow configuration to track
+ * taint from user inputs as defined by `semmle.code.cpp.security.Security`.
+ */
+
 import cpp
 import semmle.code.cpp.security.Security
 private import semmle.code.cpp.ir.dataflow.DataFlow

cpp/ql/lib/semmle/code/cpp/security/TaintTracking.qll

@@ -1,7 +1,10 @@
 /*
- * Support for tracking tainted data through the program.
+ * Support for tracking tainted data through the program. This is an alias for
+ * `semmle.code.cpp.ir.dataflow.DefaultTaintTracking` provided for backwards
+ * compatibility.
  *
- * Prefer to use `semmle.code.cpp.dataflow.TaintTracking` when designing new queries.
+ * Prefer to use `semmle.code.cpp.dataflow.TaintTracking` or
+ * `semmle.code.cpp.ir.dataflow.TaintTracking` when designing new queries.
  */
 
 import semmle.code.cpp.ir.dataflow.DefaultTaintTracking