getting_started: fix UNIX-ism

Now that the instructions work on Windows, delete a reference to
~ (the user's home on a Unix system) in the text.

Signed-off-by: Marti Bolivar <[email protected]>

Author: Marti Bolivar

doc/getting_started/getting_started.rst

@@ -28,7 +28,7 @@ using Git to clone the repository anonymously. Enter:
    git clone https://github.com/zephyrproject-rtos/zephyr.git
 
 You have successfully checked out a copy of the source code to your local
-machine in the ~/zephyr folder.
+machine in a ``zephyr`` folder in your home directory.
 
 .. _getting_started_cmake: