Improve the README.rst file. Add new screenshot and update the screencasts links.

README.rst

@@ -17,11 +17,20 @@ right where you write and test it--in a terminal. If you've worked with the
 excellent (but nowadays ancient) DOS-based Turbo Pascal or C tools, PuDB's UI
 might look familiar.
 
-Here's a screenshot:
+Here are the screenshots:
 
-.. image:: https://tiker.net/pub/pudb-screenshot.png
+* Default theme:
+    .. image:: https://tiker.net/pub/pudb-screenshot.png
 
-You may watch a `screencast <http://vimeo.com/5255125>`_, too.
+* Dark theme:
+    .. image:: ./screenshot.png
+       :height: 394px
+
+You may watch screencasts too:
+
+* `Meet Pudb, a debugger for Python code (2020) <https://www.youtube.com/watch?v=bJYkCWPs_UU>`_
+
+* `PuDB Intro Screencast (2009) <http://vimeo.com/5255125>`_
 
 Features
 --------
@@ -31,6 +40,8 @@ Features
   what's going on in your program. Variable displays can be expanded, collapsed
   and have various customization options.
 
+* Pre-bundled themes, including dark themes. Could set a custom theme also.
+
 * Simple, keyboard-based navigation using single keystrokes makes debugging
   quick and easy. PuDB understands cursor-keys and Vi shortcuts for navigation.
   Other keys are inspired by the corresponding pdb commands.