feat(cookbook): PSBTs multiple input signing

Author: storopoli

cookbook/src/SUMMARY.md

@@ -6,3 +6,6 @@
 - [Constructing and Signing Transactions](tx.md)
   - [SegWit V0](tx_segwit-v0.md)
   - [Taproot](tx_taproot.md)
+- [Working with PSBTs](psbt.md)
+    - [Constructing and Signing Multiple Inputs - SegWit V0](psbt/multiple_inputs_segwit-v0.md)
+    - [Constructing and Signing Multiple Inputs - Taproot](psbt/multiple_inputs_taproot.md)

cookbook/src/intro.md

@@ -23,6 +23,10 @@ over the peer-to-peer network, plus fun stuff you can do with miniscript.
 1. [Constructing and Signing Transactions](tx.md)
     1. [SegWit V0](tx_segwit-v0.md)
     1. [Taproot](tx_taproot.md)
+1. [Working with PSBTs](psbt.md)
+    1. Constructing and Signing Multiple Inputs:
+        1. [SegWit V0](psbt/multiple_inputs_segwit-v0.md)
+        1. [Taproot](psbt/multiple_inputs_taproot.md)
 
 ## License
 

cookbook/src/psbt.md

@@ -0,0 +1,27 @@
+# Working with PSBTs
+
+PSBTs (Partially Signed Bitcoin Transactions) are a format for encoding partially signed transactions.
+They are used in the context of multisignature wallets, hardware wallets,
+and other use cases where multiple parties need to collaborate to sign a transaction.
+
+PSBTs (version 0) are defined in [BIP 174](https://github.com/bitcoin/bips/blob/master/bip-0174.mediawiki).
+It specifies 6 different roles that a party can play in the PSBT workflow:
+
+- **Creator**: Creates the PSBT and adds inputs and outputs.
+- **Updater**: Adds additional information to the PSBT,
+  such as `redeemScript`, `witnessScript`, and BIP32 derivation paths.
+- **Signer**: Signs the PSBT, either all inputs or a subset of them.
+- **Combiner**: Combines multiple PSBTs into a single PSBT.
+- **Finalizer**: Finalizes the PSBT,
+  adding any information necessary to complete the transaction.
+- **Extractor**: Extracts the finalized transaction from the PSBT.
+
+Note that multiple roles can be handled by a single entity
+but each role is specialized in what it should be capable of doing.
+
+We provide the following examples:
+
+- [Constructing and Signing Multiple Inputs - SegWit V0](psbt/multiple_inputs_segwit-v0.md)
+- [Constructing and Signing Multiple Inputs - Taproot](psbt/multiple_inputs_taproot.md)
+
+For extra information, see the [Bitcoin Optech article on PSBTs](https://bitcoinops.org/en/topics/psbt/).