add js example (#7)

examples/nodejs-create-signing-request/README.md

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+# Nodejs create signing request example
+
+This example shows how to create a signing request using Nodejs. 
+
+Run `npm install`
+Run `node index.js`

examples/nodejs-create-signing-request/index.js

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+// const express = require('express')
+// const app = express()
+// const port = 4202
+
+// app.get('/', (req, res) => {
+//     res.send('Hello World!');
+//     console.log("Hello World");
+// })
+
+// let cors = require('cors');
+// app.use(cors())
+
+// app.listen(port, () => {
+//     console.log(`Example app listening on port ${port}`)
+// })
+
+const API_TOKEN = "YOUR-API-TOKEN";
+const grpc = require('grpc');
+const protoLoader = require('@grpc/proto-loader');
+const protobuf = require('protobufjs');
+const protoPath = './proto/api.proto';
+const packageDefinition = protoLoader.loadSync(protoPath, {
+    keepCase: true,
+    longs: String,
+    enums: String,
+    defaults: true,
+    oneofs: true
+});
+
+const protoDescriptor = grpc.loadPackageDefinition(packageDefinition);
+const PlatformAPIService = protoDescriptor.mpcvault.platform.v1.PlatformAPI;
+const client = new PlatformAPIService('api.mpcvault.com:443', grpc.credentials.createSsl());
+
+// Create metadata 
+const metadata = new grpc.Metadata();
+metadata.add('x-mtoken', API_TOKEN);
+
+const root = protobuf.loadSync(protoPath);
+const EVMGas = root.lookupType('mpcvault.platform.v1.EVMGas');
+
+// Create EVMGas
+const gasObject = {
+    maxFee: {value: '100000'}, // 使用google.protobuf.StringValue来设置值
+    maxPriorityFee: {value: '50000'},
+    gasLimit: {value: '21000'}
+};
+const evmGas = EVMGas.create(gasObject);
+
+const CreateSigningRequestRequest = {
+    evm_send_custom: {
+        "chain_id": 137, // polygon
+        "from": "0x544845005e42fE00a3C0E9735EEEC25Aa068b428", // your wallet address on MPCVault
+        "to": "", // leave empty for contract creation
+        "value": "0", // amount of tokens to send, in this case 0
+        "input": [], // contract bytecode
+        "gas_fee": evmGas, // you can leave this empty to use default gas settings
+        "nonce": {value: '0'}, // you can leave this empty to use default nonce
+    }
+}
+// send rpc request
+client.CreateSigningRequest(CreateSigningRequestRequest, metadata, (error, response) => {
+    if (error) {
+        console.log('=============error==================');
+        console.log(error);
+    } else {
+        console.log('=============response==================');
+        console.log(response);
+        // 使用 protobufjs 的 Message.decode 方法对响应进行反序列化
+    }
+});