docs/uos: Deconditionalize, remove minor port-specific details.

For a couple of ports, there was information which directory is set
as current after boot. This information doesn't belong to "uos" module,
and is moved to boards' references (which actually already contained
information on which directory is chosen for boot, even if without
explicit mentioning that it becomes current directory, which is now
done).

docs/library/uos.rst

@@ -4,28 +4,9 @@
 .. module:: uos
    :synopsis: basic "operating system" services
 
-The ``os`` module contains functions for filesystem access and ``urandom``
+The ``uos`` module contains functions for filesystem access and ``urandom``
 function.
 
-Port specifics
---------------
-
-The filesystem has ``/`` as the root directory and the
-available physical drives are accessible from here.  They are currently:
-
-    ``/flash``      -- the internal flash filesystem
-
-    ``/sd``         -- the SD card (if it exists)
-
-.. only:: port_pyboard
-
-    On boot up, the current directory is ``/flash`` if no SD card is inserted,
-    otherwise it is ``/sd``.
-
-.. only:: port_wipy
-
-    On boot up, the current directory is ``/flash``.
-
 Functions
 ---------
 

docs/pyboard/general.rst

@@ -10,7 +10,9 @@ is inserted into the slot, it is available as ``/sd``.
 
 When the pyboard boots up, it needs to choose a filesystem to boot from.  If
 there is no SD card, then it uses the internal filesystem ``/flash`` as the boot
-filesystem, otherwise, it uses the SD card ``/sd``.
+filesystem, otherwise, it uses the SD card ``/sd``. After the boot, the current
+directory is set to one of the directories above.
+
 If needed, you can prevent the use of the SD card by creating an empty file
 called ``/flash/SKIPSD``.  If this file exists when the pyboard boots
 up then the SD card will be skipped and the pyboard will always boot from the

docs/wipy/general.rst

@@ -53,7 +53,7 @@ which is stored within the external serial flash memory.  If a micro SD card
 is hooked-up and mounted, it will be available as well.
 
 When the WiPy starts up, it always boots from the ``boot.py`` located in the
-``/flash`` file system.
+``/flash`` file system. On boot up, the current directory is ``/flash``.
 
 The file system is accessible via the native FTP server running in the WiPy.
 Open your FTP client of choice and connect to: