Update chain signatures content for mainnet (#2198)

* Update chain-signatures.md

* Update chain-signatures.md

docs/1.concepts/abstraction/chain-signatures.md

@@ -13,7 +13,7 @@ This unlocks the next level of blockchain interoperability by giving ownership o
 _Diagram of a chain signature in NEAR_
 
 :::caution
-This technology is currently in `alpha` and should only be used in a `testnet` environment.
+This technology is currently in `beta` and should be used carefully and with audits on `mainnet`.
 :::
 
 ---
@@ -72,10 +72,10 @@ The essence of Multi-Party Computation (MPC) is to enable independent parties to
 
 NEAR's MPC service is comprised of several independent nodes, **none of which can sign by itself**, but instead create **signature-shares** that are **aggregated through multiple rounds** to **jointly** sign a transaction.
 
-This service continuously listens for signature requests (i.e. users calling the `sign` method on the `multichain` smart contract) and when a call is detected the MPC service:
+This service continuously listens for signature requests (i.e. users calling the `sign` method on the `v1.signer` smart contract) and when a call is detected the MPC service:
 
   1. Asks its nodes to jointly derive a signature for the `payload` using the account identified by the `path`
-  2. Once complete, call the `multichain` contract to store the resulting `Signature`
+  2. Once complete, call the `v1.signer` contract to store the resulting `Signature`
 
 :::info A Custom MPC Service
 Generally, MPC signing services work by sharing a master key, which needs to be re-created each time a node joins or leaves.

docs/2.build/1.chain-abstraction/chain-signatures.md

@@ -31,7 +31,7 @@ There are five steps to create a Chain Signature:
 
 1. [Deriving the Foreign Address](#1-deriving-the-foreign-address) - Construct the address that will be controlled on the target blockchain
 2. [Creating a Transaction](#2-creating-the-transaction) - Create the transaction or message to be signed
-3. [Requesting a Signature](#3-requesting-the-signature) - Call the NEAR `multichain` contract requesting it to sign the transaction
+3. [Requesting a Signature](#3-requesting-the-signature) - Call the NEAR `v1.signer` contract requesting it to sign the transaction
 4. [Reconstructing the Signature](#4-reconstructing-the-signature) - Reconstruct the signature from the MPC service's response
 5. [Relaying the Signed Transaction](#5-relaying-the-signature) - Send the signed transaction to the destination chain for execution
 
@@ -48,6 +48,12 @@ If you want to try things out, these are the smart contracts available on `testn
 
 :::
 
+:::info MPC mainnet contracts
+
+- `v1.signer`: [MPC signer](https://github.com/near/mpc/tree/v0.2.0/contract) contract, latest release, made up of 8 MPC nodes
+
+:::
+
 ---
 
 ## 1. Deriving the Foreign Address