docs: add app icon and demo image to readme #83

Job	Run time
lint	21s
changes	6s
Rust tests (macOS)	1m 55s
Rust tests (Windows)	5m 0s
typecheck	25s
test-js	56s
Rust tests (Linux)	1m 44s
Tauri build (${{ matrix.platform.name }})	0s
	10m 27s

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