Add test-obj to the help message

src/main.zig

@@ -87,6 +87,7 @@ const normal_usage =
     \\  build-lib        Create library from source or object files
     \\  build-obj        Create object from source or object files
     \\  test             Perform unit testing
+    \\  test-obj         Create object for unit testing
     \\  run              Create executable and run immediately
     \\
     \\  ast-check        Look for simple compile errors in any set of files