Update PARALLEL parameter in testJobTemplate

buildenv/jenkins/testJobTemplate

@@ -376,9 +376,10 @@ ARCH_OS_LIST.each { ARCH_OS ->
 							    sectionHeaderStyle(sectionHeaderHelpTextStyleCss)
 							}
 							choiceParam('PARALLEL', PARALLEL_LIST, "Optional. Parallel mode")
-							stringParam('NUM_MACHINES', NUM_MACHINES, '''Optional. It has to be used with PARALLEL=Dynamic or PARALLEL=NodesByIterations<br/>
-							Use with PARALLEL=Dynamic, NUM_MACHINES cannot be greater than the number of matched nodes on Jenkins<br/>
-							Use with PARALLEL=NodesByIterations, NUM_MACHINES cannot be greater than 20<br/>''')
+							stringParam('NUM_MACHINES', NUM_MACHINES, '''Optional. Parallel mode: <br/>None // run test(s) in serial <br/>
+							Dynamic // dynamically divides tests according to NUM_MACHINES and runs them in parallel. Please also provide NUM_MACHINES. <br/>
+							NodesByIterations // run the same test(s) in parallel according to NUM_MACHINES. You can also provide ITERATIONS. This is mainly for debugging intermittent issues. <br/>
+							Subdir // run tests in parallel according to subdir. This is mainly for external tests.''')
 							stringParam('TEST_TIME', TEST_TIME, '''Optional. Expected overall test build execution time. Needs to be used with PARALLEL=Dynamic.<br>
 							Once TEST_TIME is provided, test pipeline will automatically run tests in parallel and try to achieve the expected TEST_TIME.<br>
 							To ensure a balanced workload in test child builds, please also provide TRSS_URL.<br>