docs: add real screenshot to README, alongside the ASCII diagram

Referenced via the raw.githubusercontent.com absolute URL rather than
a relative path - README.md doubles as the PyPI long_description
(confirmed earlier this project embeds correctly there), and PyPI
doesn't resolve relative image paths against the repo, only absolute
URLs work in both places. ASCII diagram kept as a text-only fallback
(pip show, plain-text viewers, anywhere images don't render).

Author: andlo

README.md

@@ -10,6 +10,11 @@ Actively maintained. The core experience is stable today and it's a solid, worki
 
 ## What it looks like
 
+![ovos-tui-client screenshot](https://raw.githubusercontent.com/andlo/ovos-tui-client/main/ovos-tui-client.png)
+
+The four panes in text form, for anywhere images don't render (a
+plain-text README viewer, `pip show`, etc):
+
 ```
 ┌──────────────────────────────────────────┐
 │ Sources: [X]bus [X]skills [X]audio ...    │