Add missing predicate qldoc

Author: rvermeulen

java/ql/src/semmle/code/java/security/LdapInjection.qll

@@ -19,6 +19,10 @@ abstract class LdapInjectionSanitizer extends DataFlow::Node { }
  * Extend this class to add additional taint steps that should apply to the LdapInjectionFlowConfig.
  */
 class LdapInjectionAdditionalTaintStep extends TaintTracking::Unit {
+  /**
+   * Holds if the step from `node1` to `node2` should be considered a taint
+   * step for the LdapInjectionFlowConfig configuration.
+   */
   abstract predicate step(DataFlow::Node node1, DataFlow::Node node2);
 }