add GUI image to main docs page and README

Author: SBlokhuizen

README.md

@@ -6,6 +6,10 @@ are described using descriptive tendencies, such as sine waves or linear ramps.
 Waveform Editor includes a GUI for interactive creation, editing, and organization of
 waveforms.
 
+| ![GUI of the Waveform Editor](docs/source/images/gui/editor.png) |
+|:--:|
+| GUI of the Waveform Editor |
+
 ## Development Status 
 
 This project is currently under active development. While a functional prototype and

docs/source/index.rst

@@ -4,6 +4,10 @@ Waveform Editor manual
 
 The Waveform Editor is a Python tool for creating and managing 1D time-dependent data called waveforms. It utilizes a human-readable, text-based file format where waveforms are described using descriptive tendencies, such as sine waves or linear ramps. The Waveform Editor includes a GUI for interactive creation, editing, and organization of waveforms.
 
+.. figure:: images/gui/editor.png
+
+   GUI of the Waveform Editor.
+
 Manual
 ------