Add missing qldocs for two isVariadic() predicates

ql/lib/semmle/go/Decls.qll

@@ -137,6 +137,7 @@ class FuncDef extends @funcdef, StmtParent, ExprParent {
    */
   DataFlow::CallNode getACall() { result.getACallee() = this }
 
+  /** Holds if this function is variadic. */
   predicate isVariadic() { this.getType().isVariadic() }
 
   override string getAPrimaryQlClass() { result = "FuncDef" }

ql/lib/semmle/go/Scopes.qll

@@ -377,6 +377,7 @@ class Function extends ValueEntity, @functionobject {
   /** Gets the declaration of this function, if any. */
   FuncDecl getFuncDecl() { none() }
 
+  /** Holds if this function is variadic. */
   predicate isVariadic() {
     this.(BuiltinFunction).getName() = ["append", "make", "print", "println"]
     or