python3Packages.tkinter: Improve meta.description (#239047)

pkgs/development/python-modules/tkinter/default.nix

···
     patchelf --set-rpath $new_rpath $out/${py.sitePackages}/_tkinter*
   '';
 
-  meta = py.meta;
+  meta = py.meta // {
+    # Based on first sentence from https://docs.python.org/3/library/tkinter.html
+    description = "The standard Python interface to the Tcl/Tk GUI toolkit";
+    longDescription = ''
+      The tkinter package (“Tk interface”) is the standard Python interface to
+      the Tcl/Tk GUI toolkit. Both Tk and tkinter are available on most Unix
+      platforms, including macOS, as well as on Windows systems.
+
+      Running python -m tkinter from the command line should open a window
+      demonstrating a simple Tk interface, letting you know that tkinter is
+      properly installed on your system, and also showing what version of
+      Tcl/Tk is installed, so you can read the Tcl/Tk documentation specific to
+      that version.
+
+      Tkinter supports a range of Tcl/Tk versions, built either with or without
+      thread support. The official Python binary release bundles Tcl/Tk 8.6
+      threaded. See the source code for the _tkinter module for more
+      information about supported versions.
+
+      Tkinter is not a thin wrapper, but adds a fair amount of its own logic to
+      make the experience more pythonic. This documentation will concentrate on
+      these additions and changes, and refer to the official Tcl/Tk
+      documentation for details that are unchanged.
+    '';
+  };
 
 }