Add missing qldocs

Author: owen-mc

go/ql/lib/semmle/go/controlflow/IR.qll

@@ -446,6 +446,7 @@ module IR {
     /** Gets the target to which this instruction writes. */
     WriteTarget getLhs() { result = lhs }
 
+    /** Holds if this instruction initializes a literal. */
     predicate isInitialization() { initialization = true }
 
     /** Gets the instruction computing the value this instruction writes. */

go/ql/lib/semmle/go/dataflow/internal/DataFlowNodes.qll

@@ -817,6 +817,7 @@ module Public {
     abstract Node getPreUpdateNode();
   }
 
+  /** Holds if the node corresponding to `insn` has a post-update node. */
   predicate insnHasPostUpdateNode(IR::Instruction insn) {
     exists(Expr e | insn.(IR::EvalInstruction).getExpr() = e |
       e instanceof AddressExpr or