Added draft for claim

Author: lucasvo

README.md

@@ -75,6 +75,7 @@ Where message `type` must be one of:
 - `3`: `TeleportAsset`
 - `32`: `RelayMessageParachain`
 - `33`: `ParachainRelayMessage`
+- `42`: `AccountClaim`
 
 Within XCM version 0, there is a secondary datatype `Ai`, "Asset Instruction", defined as:
 
@@ -208,6 +209,14 @@ Initiates a `Balances` message to some `destination` with the given `query_id` f
 - `destination: MultiLocation` Recipient of the `Balances` message.
 - `assets: Vec<MultiAsset>` Asset(s) to be queried. Use of wildcards (empty/zero/`Undefined` identifiers) should generally be supported.
 
+### `AccountClaim`
+Sends a claim verified to be from the `source` to the `destination` on the parachain. It has an `expiration` timestamp and a `scope` used to define the scope under which such a `claim` is made. A chain should only send such a claim if it is verified to have been intended to be sent by the `source`. It facilitates authentication across parachains.
+
+- `source: MultiLocation`
+- `destination: MultiLocation`
+- `timestamp: Compact<u48>`
+- `scope: Vec<u8>`
+
 ## `MultiAsset`: Universal Asset Identifiers
 
 Basic format: