docs: add documentation of eth_call overrides

src/chains/ethereum/ethereum/RPC-METHODS.md

@@ -155,6 +155,16 @@ Executes a new message call immediately without creating a transaction on the bl
 
 - `transaction: any` : The transaction call object as seen in source.
 - `blockNumber: QUANTITY | TAG` : Integer block number, or the string "latest", "earliest" or "pending".
+- `overrides: CallOverrides`: State overrides to apply during the simulation.
+ - `CallOverrides` - An address-to-state mapping, where each entry specifies some
+state to be ephemerally overridden prior to executing the call. Each address maps to an object containing:
+ - `balance: QUANTITY` (optional) - The balance to set for the account before executing the call.
+ - `nonce: QUANTITY` (optional) - The nonce to set for the account before executing the call.
+ - `code: DATA` (optional) - The EVM bytecode to set for the account before executing the call.
+ - `state: OBJECT` (optional\*) - Key-value mapping to override _all_ slots in the account storage before executing the call.
+ - `stateDiff: OBJECT` (optional\*) - Key-value mapping to override _individual_ slots in the account storage before executing the call.
+
+ _\*Note - `state` and `stateDiff` fields are mutually exclusive._
 
 ##### Returns