doc: Add musig() example

Author: achow101

doc/descriptors.md

@@ -69,6 +69,7 @@ Output descriptors currently support:
 - `tr(c6047f9441ed7d6d3045406e95c07cd85c778e4b8cef3ca7abac09b95c709ee5,sortedmulti_a(2,2f8bde4d1a07209355b4a7250a5c5128e88b84bddc619ab7cba8d569b240efe4,5cbdf0646e5db4eaa398f365f2ea7a0e3d419b7e0330e39ce92bddedcac4f9bc))` describes a P2TR output with the `c6...` x-only pubkey as internal key, and a single `multi_a` script that needs 2 signatures with 2 specified x-only keys, which will be sorted lexicographically.
 - `wsh(sortedmulti(2,[6f53d49c/44h/1h/0h]tpubDDjsCRDQ9YzyaAq9rspCfq8RZFrWoBpYnLxK6sS2hS2yukqSczgcYiur8Scx4Hd5AZatxTuzMtJQJhchufv1FRFanLqUP7JHwusSSpfcEp2/0/*,[e6807791/44h/1h/0h]tpubDDAfvogaaAxaFJ6c15ht7Tq6ZmiqFYfrSmZsHu7tHXBgnjMZSHAeHSwhvjARNA6Qybon4ksPksjRbPDVp7yXA1KjTjSd5x18KHqbppnXP1s/0/*,[367c9cfa/44h/1h/0h]tpubDDtPnSgWYk8dDnaDwnof4ehcnjuL5VoUt1eW2MoAed1grPHuXPDnkX1fWMvXfcz3NqFxPbhqNZ3QBdYjLz2hABeM9Z2oqMR1Gt2HHYDoCgh/0/*))#av0kxgw0` describes a *2-of-3* multisig. For brevity, the internal "change" descriptor accompanying the above external "receiving" descriptor is not included here, but it typically differs only in the xpub derivation steps, ending in `/1/*` for change addresses.
 - `wsh(thresh(4,pk([7258e4f9/44h/1h/0h]tpubDCZrkQoEU3845aFKUu9VQBYWZtrTwxMzcxnBwKFCYXHD6gEXvtFcxddCCLFsEwmxQaG15izcHxj48SXg1QS5FQGMBx5Ak6deXKPAL7wauBU/0/*),s:pk([c80b1469/44h/1h/0h]tpubDD3UwwHoNUF4F3Vi5PiUVTc3ji1uThuRfFyBexTSHoAcHuWW2z8qEE2YujegcLtgthr3wMp3ZauvNG9eT9xfJyxXCfNty8h6rDBYU8UU1qq/0/*),s:pk([4e5024fe/44h/1h/0h]tpubDDLrpPymPLSCJyCMLQdmcWxrAWwsqqssm5NdxT2WSdEBPSXNXxwbeKtsHAyXPpLkhUyKovtZgCi47QxVpw9iVkg95UUgeevyAqtJ9dqBqa1/0/*),s:pk([3b1d1ee9/44h/1h/0h]tpubDCmDTANBWPzf6d8Ap1J5Ku7J1Ay92MpHMrEV7M5muWxCrTBN1g5f1NPcjMEL6dJHxbvEKNZtYCdowaSTN81DAyLsmv6w6xjJHCQNkxrsrfu/0/*),sln:after(840000),sln:after(1050000),sln:after(1260000)))#k28080kv` describes a Miniscript multisig with spending policy: `thresh(4,pk(key_1),pk(key_2),pk(key_3),pk(key_4),after(t1),after(t2),after(t3))` that starts as 4-of-4 and "decays" to 3-of-4, 2-of-4, and finally 1-of-4 at each future halvening block height. For brevity, the internal "change" descriptor accompanying the above external "receiving" descriptor is not included here, but it typically differs only in the xpub derivation steps, ending in `/1/*` for change addresses.
+- `tr(musig(xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL,xpub68NZiKmJWnxxS6aaHmn81bvJeTESw724CRDs6HbuccFQN9Ku14VQrADWgqbhhTHBaohPX4CjNLf9fq9MYo6oDaPPLPxSb7gwQN3ih19Zm4Y)/0/*)` describes a MuSig2 multisig with key derivation. The internal keys are derived at `m/0/*` from the aggregate key computed from the 2 participants.
 
 ## Reference