update readme file

Author: AlaaElattar

packages/tfchain_client/README.md

@@ -16,23 +16,41 @@ There are 2 types of client. one for just query the chain and the other one for
 import 'package:tfchain_client/tfchain_client.dart';
 
 final client = QueryClient("wss://tfchain.dev.grid.tf/ws");
-client.connect();
+await client.connect();
 final contract = await client.contracts.get(contractId: BigInt.from(123456));
 print(contract!.toJson());
-client.disconnect();
+await client.disconnect();
 ```
 
 ### Full Client
 
 ```dart
-final client = Client("wss://tfchain.dev.grid.tf/ws", "your-mnemonic");
+final client = Client("wss://tfchain.dev.grid.tf/ws", "your-mnemonic", "sr25519");
 client.connect();
-final extrinsic = await client.clientFarms.create(CreateFarmOptions(name: "name"));
-await client.apply(extrinsic);
-client.disconnect();
+final farmId = await client.farma.create(CreateFarmOptions(name: "name"));
+print(farmId);
+await client.disconnect();
 ```
 
 ## Run Tests
+### Prerequisites
+
+1- Provide your mnemonic as environment variable.
+```bash
+export MNEMONIC="your-mnemonic"
+```
+2- provide chain url and the signing type.
+By default the chain url is set to `wss://tfchain.dev.grid.tf/ws` and the signing type is `sr25519`. Note that signing type can be either `sr25519` or `ed25519`.
+```bash
+export LINK="chain_url"
+```
+```bash
+export SIGN_TYPE="sr25519"
+```
+
+
+
+
 
 To run the tests, run the following command