docs: add app icon and demo image to readme #82

Job	Run time
changes	6s
test-js	1m 0s
Rust tests (Windows)	4m 23s
lint	19s
Rust tests (Linux)	1m 44s
typecheck	26s
Rust tests (macOS)	1m 50s
Tauri build (${{ matrix.platform.name }})	0s
	9m 48s

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