doc: Add some documentation about process and directory structure

README.md

@@ -1,3 +1,21 @@
 This repository contains Guix attestations for releases of Bitcoin Core.
 
+## Overall process
+
+The Guix build consists of two stages:
+
+- In the first stage (`noncodesigned`), people compile the binaries from source.
+- Then, code signatures for Windows and MacOS are generated from the binaries that were produced in the first stage, and [distributed](https://github.com/bitcoin-core/bitcoin-detached-sigs) to the builders.
+- In the second stage (`all`), the builders attach these code signatures.
+
 See https://github.com/bitcoin/bitcoin/blob/master/doc/release-process.md#building on how to build the release with Guix and create an attestation.
+
+## Directory structure
+
+- `/<version>/<signer>/`: Build attestations for repository tag `v<version>` for `<signer>`.
+    - `noncodesigned.SHA256SUMS`: Hashes of binaries produced by the first stage build for this version.
+    - `noncodesigned.SHA256SUMS.asc`: Detached PGP signature for `noncodesigned.SHA256SUMS`.
+    - `all.SHA256SUMS`: Hashes of binaries produced by the second stage build. This covers all the binaries uploaded to the website, and is what to check release binaries against.
+    - `all.SHA256SUMS.asc`: Detached PGP signature for `all.SHA256SUMS`.
+- `/builder-keys/<signer>.gpg`: PGP keys of the signers. If you're going to do builds and contribute attestations, file a PR to add your key here.
+- `/contrib`: Scripts used in the CI tests.