Raw documentation for the bdist_wininst postinstallation script.

People are already using it, so these docs are certainly better than
no docs at all. Markup is mostly missing and the layout is probably
ugly, but this can be fixed later.

Question: there are references to MS docs for the CSIDL_... constants
and the IShellLink interface. Are these pointers sufficient, or should
the MS docs reworded and repeated here?

Doc/dist/dist.tex

@@ -1315,6 +1315,84 @@ The installer file will be written to the ``distribution directory''
 --- normally \file{dist/}, but customizable with the
 \longprogramopt{dist-dir} option.
 
+\subsubsection{The Postinstallation script}
+\label{postinstallation-script}
+
+Starting with Python 2.3, a postinstallation script can be specified
+which the \longprogramopt{install-script} option.  The basename of the
+script must be specified, and the script filename must also be listed
+in the scripts argument to the setup function.
+
+This script will be run at installation time on the target system
+after all the files have been copied, with argv[1] set to '-install',
+and again at uninstallation time before the files are removed with argv[1]
+set to '-remove'.
+
+The installation script runs embedded in the windows installer, every
+output (sys.stdout, sys.stderr) is redirected into a buffer and will
+be displayed in the GUI after the script has finished.
+
+Some functions especially useful in this context are available in the
+installation script.
+
+\begin{verbatim}
+dir_created(pathname)
+file_created(pathname)
+\end{verbatim}
+
+These functions should be called when a directory or file is created
+by the postinstall script at installation time.  It will register the
+pathname with the uninstaller, so that it will be removed when the
+distribution is uninstalled.  To be safe, directories are only removed
+if they are empty.
+
+\begin{verbatim}
+get_special_folder_path(csidl_string)
+\end{verbatim}
+
+This function can be used to retrieve special folder locations on
+Windows like the Start Menu or the Desktop.  It returns the full path
+to the folder.  'csidl_string' must be on of the following strings:
+
+\begin{verbatim}
+"CSIDL_APPDATA"
+
+"CSIDL_COMMON_STARTMENU"
+"CSIDL_STARTMENU"
+
+"CSIDL_COMMON_DESKTOPDIRECTORY"
+"CSIDL_DESKTOPDIRECTORY"
+
+"CSIDL_COMMON_STARTUP"
+"CSIDL_STARTUP"
+
+"CSIDL_COMMON_PROGRAMS"
+"CSIDL_PROGRAMS"
+
+"CSIDL_FONTS"
+\end{verbatim}
+
+If the folder cannot be retrieved, OSError is raised.
+
+Which folders are available depends on the exact Windows version, and probably
+also the configuration. For details refer to Microsoft's documentation of the
+SHGetSpecialFolderPath function.
+
+\begin{verbatim}
+create_shortcut(target, description, filename[, arguments[,
+                workdir[, iconpath[, iconindex]]]])
+\end{verbatim}
+
+This function creates a shortcut.
+target is the path to the program to be started by the shortcut.
+description is displayed in a popup window when the
+filename is the title of the shortcut that the user will see.
+arguments specifies the command line arguments, if any.
+workdir is the working directory for the program.
+iconpath is the file containing the icon for the shortcut,
+and iconindex is the iconindex in the file.
+Again, for details consult the Microsoft documentation for the IShellLink
+interface.
 
 \section{Examples}
 \label{examples}