Add Bitcoin V-App architecture docs #154

Job	Run time
vnd-test, Build on Risc-V target	22s
vnd-sadik, Build on Risc-V target	24s
Run V-App SDK tests	23s
Run V-App Client SDK tests	35s
Run common crate tests	19s
Run vnd-test app tests	21s
Run vnd-bitcoin app tests	25s
Run vnd-test app client tests	41s
Build application using the reusable workflow / Retrieve application metadata / Retrieve application metadata	8s
Build application using the reusable workflow / Build application for NanoS, X, S+, and Stax (flex)	2m 28s
Build application using the reusable workflow / Build application for NanoS, X, S+, and Stax (stax)	2m 30s
Build application using the reusable workflow / Build application for NanoS, X, S+, and Stax (nanosp)	2m 18s
Build application using the reusable workflow / Merge build artifacts	2s
vnd-test, Integration tests on Speculos (nanosplus)	2m 4s
vnd-sadik, Integration tests on Speculos (nanosplus)	5m 43s
vnd-test, Integration tests on Speculos (flex)	1m 56s
vnd-sadik, Integration tests on Speculos (flex)	5m 44s
vnd-test, Integration tests on Speculos (stax)	2m 6s
vnd-sadik, Integration tests on Speculos (stax)	6m 7s
	34m 36s

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