Mark up environment variables

docs/starting/install/osx.rst

@@ -46,7 +46,7 @@ simply run
 The script will explain what changes it will make and prompt you before the
 installation begins.
 Once you've installed Homebrew, insert the Homebrew directory at the top
-of your ``PATH`` environment variable. You can do this by adding the following
+of your :envvar:`PATH` environment variable. You can do this by adding the following
 line at the bottom of your :file:`~/.bashrc` file
 
 .. code-block:: console
@@ -60,7 +60,7 @@ Now, we can install Python 2.7:
     $ brew install python
 
 This will take a minute or two. Once that's complete, you'll have to add the
-new Python scripts directory to your ``PATH``
+new Python scripts directory to your :envvar:`PATH`
 
 .. code-block:: console
 

docs/starting/install/win.rst

@@ -17,13 +17,13 @@ e.g. Python version 2.7 will install at :file:`C:\Python27\`, so that you can
 have multiple versions of Python on the
 same system without conflicts. Of course, only one interpreter can be the
 default application for Python file types. It also does not automatically
-modify the ``PATH`` environment variable, so that you always have control over
+modify the :envvar:`PATH` environment variable, so that you always have control over
 which copy of Python is run.
 
 Typing the full path name for a Python interpreter each time quickly gets
-tedious, so add the directories for your default Python version to the PATH.
+tedious, so add the directories for your default Python version to the :envvar:`PATH`.
 Assuming that your Python installation is in :file:`C:\Python27\`, add this to your
-PATH:
+:envvar:`PATH`:
 
 .. code-block:: console