Add /lib to the PATH variable for running examples

[eliemichel]

At least on Windows it is required

Description of Change(s)

In the tutorial's Environment Setup section, which is where a lot of newcomers pass by, one is advised to add to the PATH variable the binary directory USD_INSTALL_ROOT/bin, but USD_INSTALL_ROOT/lib is actually required (at least on Windows), without what the following issue is encountered:

C:\Users\emichel\SourceCode>usdview USD/extras/usd/tutorials/convertingLayerFormats/Sphere.usda
Traceback (most recent call last):
  File "C:\Users\emichel\SourceCode\USD_install\bin\usdview", line 28, in <module>
    import pxr.Usdviewq as Usdviewq
  File "C:\Users\emichel\SourceCode\USD_install\lib\python\pxr\Usdviewq\__init__.py", line 27, in <module>
    from pxr import Tf
  File "C:\Users\emichel\SourceCode\USD_install\lib\python\pxr\Tf\__init__.py", line 163, in <module>
    PreparePythonModule()
  File "C:\Users\emichel\SourceCode\USD_install\lib\python\pxr\Tf\__init__.py", line 88, in PreparePythonModule
    module = importlib.import_module(
             ^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Python311\Lib\importlib\__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ImportError: DLL load failed while importing _tf: The specified module could not be found.

• I have submitted a signed Contributor License Agreement

[sunyab]

Filed as internal issue #USD-7917