testing GC with sweeptool

## Abstract

For non-coders with some CLI knowledge. Also iOS 13 or higher needed.

We want to test if `sweeptool-cli` and [Gordian Cosigner](https://github.com/BlockchainCommons/GordianCosigner-iOS) app are interoperable.

* First, install Gordian Cosigner (GC) and familiarize with it (try to create/import cosigners, create an account map, a psbt etc.)
* In Gordian Cosigner we can export an account (Bitcoin output descriptor) (*) and import it into `sweeptool-cli` to see if it works.
* For example, working with GC in testnet mode, you can first try to create an account with 2 cosigners created from seed or bip39 words. Then try to send some testnet coins to that account (google for a testnet faucet). Export that account into `sweeptool-cli` and sweep those funds to any address of your liking. The sweeptool-cli will create a PSBT for you which you can import back into GC and sign it with your cosigners. Can the transaction actually be signed and broadcast? Show and document the steps you've taken and PR a document. Report if you run into problems.

/* the app may export a descriptor without a tail (1/* and 0/*) which should be appended manually, make notes

Bonus work: come up with more test scenarios

Installez Gordian Cosigner sur iOS 13 ou une version ultérieure et utilisez sweeptool-cli avec un compte de testnet exporté sous forme de descripteur de sortie Bitcoin. Suivez le flux de création, de financement, d’exportation, de sweep, d’importation, de signature et de broadcast de l’issue, en notant toute terminaison du descripteur qui doit être ajoutée. Documentez les étapes et les résultats exacts dans un PR, y compris les problèmes et tous les scénarios bonus testés.

Rédigé par le modèle d'indexation à partir du texte de l'issue.