lib: add missing env vars to --help

PR-URL: https://github.com/nodejs/node/pull/43492
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Feng Yu <F3n67u@outlook.com>

lib/internal/main/print_help.js

@@ -55,10 +55,15 @@ const envVars = new SafeMap(ArrayPrototypeConcat([
     'of stderr' }],
   ['NODE_REPL_HISTORY', { helpText: 'path to the persistent REPL ' +
     'history file' }],
+  ['NODE_REPL_EXTERNAL_MODULE', { helpText: 'path to a Node.js module ' +
+    'which will be loaded in place of the built-in REPL' }],
+  ['NODE_SKIP_PLATFORM_CHECK', { helpText: 'set to 1 to skip ' +
+    'the check for a supported platform during Node.js startup' }],
   ['NODE_TLS_REJECT_UNAUTHORIZED', { helpText: 'set to 0 to disable TLS ' +
     'certificate validation' }],
   ['NODE_V8_COVERAGE', { helpText: 'directory to output v8 coverage JSON ' +
     'to' }],
+  ['TZ', { helpText: 'specify the timezone configuration' }],
   ['UV_THREADPOOL_SIZE', { helpText: 'sets the number of threads used in ' +
     'libuv\'s threadpool' }],
 ], hasIntl ? [