chore: Fix usage text for embedded mode

Fixes: #19

lib/_inspect.js

@@ -24,8 +24,10 @@ const { spawn } = require('child_process');
 const { EventEmitter } = require('events');
 const util = require('util');
 
+const runAsStandalone = typeof __dirname !== 'undefined';
+
 const [ InspectClient, createRepl ] =
-  (typeof __dirname !== 'undefined') ?
+  runAsStandalone ?
   // This copy of node-inspect is on-disk, relative paths make sense.
   [
     require('./internal/inspect_client'),
@@ -258,8 +260,12 @@ function startInspect(argv = process.argv.slice(2),
                       stdout = process.stdout) {
   /* eslint-disable no-console */
   if (argv.length < 1) {
-    console.error('Usage: node-inspect script.js');
-    console.error('       node-inspect <host>:<port>');
+    const invokedAs = runAsStandalone ?
+      'node-inspect' :
+      `${process.argv0} ${process.argv[1]}`;
+
+    console.error(`Usage: ${invokedAs} script.js`);
+    console.error(`       ${invokedAs} <host>:<port>`);
     process.exit(1);
   }