docs: add Multisig docs

Author: JuArce

README_INFRASTRUCTURE.md

@@ -8,6 +8,7 @@
   - [Explorer](#explorer)
   - [Notes on project creation / devnet deployment](#notes-on-project-creation--devnet-deployment)
   - [Tests](#tests)
+  - [Multisig Usage](#multisig-usage)
 
 ## Local Devnet Setup
 
@@ -788,3 +789,46 @@ To run the go tests
 ```bash
 make test
 ```
+
+## Multisig Usage
+
+You can create a Multisig wallet using [Safe](https://safe.global/).
+
+Once you have a Multisig, you can deploy the contracts using the Multisig wallet address as the upgrader, pauser, etc.
+
+In order to upgrade a contract using the Multisig, you have to run:
+
+```bash
+make upgrade_aligned_contracts
+```
+
+Then, if the new implementation is correctly deployed, the script will show the following message:
+
+```bash
+To send the transaction using multisig use this calldata
+<calldata>
+```
+
+You can use this calldata to send the transaction using the Multisig wallet in the transaction builder provided by Safe
+
+![multisig_1.png](images/multisig_1.png)
+
+For example, if you are upgrading the ServiceManager, fill the data with the ProxyAdmin address and ABI
+
+To get the ProxyAdmin address for Holesky you can run
+
+```bash
+jq -r ".addresses.alignedLayerProxyAdmin" contracts/script/output/holesky/alignedlayer_deployment_output.json | pbcopy
+```
+
+To get the ABI you can run
+
+```bash
+jq ".abi" contracts/out/ProxyAdmin.sol/ProxyAdmin.json | pbcopy
+```
+
+Then, you can paste the ABI in the ABI field
+
+![multisig_2.png](images/multisig_2.png)
+
+If the transaction is correctly created, you have to wait until required Multisig member sign the transaction to send it