docs/library/index.rst: Minimally adapt for unix port.

docs/library/index.rst

@@ -17,6 +17,19 @@ The following standard Python libraries are built in to MicroPython.
 For additional libraries, please download them from the `micropython-lib repository
 <https://github.com/micropython/micropython-lib>`_.
 
+.. only:: port_unix
+
+    .. toctree::
+       :maxdepth: 1
+    
+       cmath.rst
+       gc.rst
+       math.rst
+       os.rst
+       struct.rst
+       sys.rst
+       time.rst
+
 .. only:: port_pyboard
 
     .. toctree::
@@ -50,13 +63,15 @@ the philosophy of MicroPython.  They provide the core functionality of that
 module and are intended to be a drop-in replacement for the standard Python
 library.
 
+.. only:: not port_unix
+
     The modules are available by their u-name, and also by their non-u-name.  The
     non-u-name can be overridden by a file of that name in your package path.
     For example, ``import json`` will first search for a file ``json.py`` or
     directory ``json`` and load that package if it is found.  If nothing is found,
     it will fallback to loading the built-in ``ujson`` module.
 
-.. only:: port_pyboard
+.. only:: port_pyboard or port_unix
 
    .. toctree::
       :maxdepth: 1