Update README, add deprecation warning

Author: junderw

README.md

@@ -85,6 +85,14 @@ The below examples are implemented as integration tests, they should be very eas
 Otherwise, pull requests are appreciated.
 Some examples interact (via HTTPS) with a 3rd Party Blockchain Provider (3PBP).
 
+### Warning: Currently the tests use TransactionBuilder, which will be removed in the future (v6.x.x or higher)
+We will move towards replacing all instances of TransactionBuilder in the tests with the new Psbt.
+
+Currently we have a few examples on how to use the newer Psbt class at the following link:
+- [Psbt examples](https://github.com/bitcoinjs/bitcoinjs-lib/blob/master/test/integration/transactions-psbt.js)
+
+The rest of the examples are below (using TransactionBuilder for Transaction creation)
+
 - [Generate a random address](https://github.com/bitcoinjs/bitcoinjs-lib/blob/master/test/integration/addresses.js)
 - [Import an address via WIF](https://github.com/bitcoinjs/bitcoinjs-lib/blob/master/test/integration/addresses.js)
 - [Generate a 2-of-3 P2SH multisig address](https://github.com/bitcoinjs/bitcoinjs-lib/blob/master/test/integration/addresses.js)

src/transaction_builder.js

@@ -57,6 +57,13 @@ class TransactionBuilder {
     this.__TX = new transaction_1.Transaction();
     this.__TX.version = 2;
     this.__USE_LOW_R = false;
+    console.warn(
+      'Deprecation Warning: TransactionBuilder will be removed in the future. ' +
+        '(v6.x.x or later) Please use the Psbt class instead. Examples of usage ' +
+        'are available in the transactions-psbt.js integration test file on our ' +
+        'Github. A high level explanation is available in the psbt.ts and psbt.js ' +
+        'files as well.',
+    );
   }
   static fromTransaction(transaction, network) {
     const txb = new TransactionBuilder(network);

test/integration/cltv.js

@@ -7,6 +7,7 @@ const bip65 = require('bip65')
 
 const alice = bitcoin.ECPair.fromWIF('cScfkGjbzzoeewVWmU2hYPUHeVGJRDdFt7WhmrVVGkxpmPP8BHWe', regtest)
 const bob = bitcoin.ECPair.fromWIF('cMkopUXKWsEzAjfa1zApksGRwjVpJRB3831qM9W4gKZsLwjHXA9x', regtest)
+console.warn = () => {} // Silence the Deprecation Warning
 
 describe('bitcoinjs-lib (transactions w/ CLTV)', () => {
   // force update MTP

test/integration/csv.js

@@ -9,6 +9,7 @@ const alice = bitcoin.ECPair.fromWIF('cScfkGjbzzoeewVWmU2hYPUHeVGJRDdFt7WhmrVVGk
 const bob = bitcoin.ECPair.fromWIF('cMkopUXKWsEzAjfa1zApksGRwjVpJRB3831qM9W4gKZsLwjHXA9x', regtest)
 const charles = bitcoin.ECPair.fromWIF('cMkopUXKWsEzAjfa1zApksGRwjVpJRB3831qM9W4gKZsMSb4Ubnf', regtest)
 const dave = bitcoin.ECPair.fromWIF('cMkopUXKWsEzAjfa1zApksGRwjVpJRB3831qM9W4gKZsMwS4pqnx', regtest)
+console.warn = () => {} // Silence the Deprecation Warning
 
 describe('bitcoinjs-lib (transactions w/ CSV)', () => {
   // force update MTP

test/integration/payments.js

@@ -7,6 +7,7 @@ const keyPairs = [
   bitcoin.ECPair.makeRandom({ network: NETWORK }),
   bitcoin.ECPair.makeRandom({ network: NETWORK })
 ]
+console.warn = () => {} // Silence the Deprecation Warning
 
 async function buildAndSign (depends, prevOutput, redeemScript, witnessScript) {
   const unspent = await regtestUtils.faucetComplex(prevOutput, 5e4)

test/integration/transactions.js

@@ -3,6 +3,7 @@ const assert = require('assert')
 const bitcoin = require('../../')
 const regtestUtils = require('./_regtest')
 const regtest = regtestUtils.network
+console.warn = () => {} // Silence the Deprecation Warning
 
 function rng () {
   return Buffer.from('YT8dAtK4d16A3P1z+TpwB2jJ4aFH3g9M1EioIBkLEV4=', 'base64')

test/transaction_builder.js

@@ -9,6 +9,8 @@ const Transaction = require('..').Transaction
 const TransactionBuilder = require('..').TransactionBuilder
 const NETWORKS = require('../src/networks')
 
+console.warn = () => {} // Silence the Deprecation Warning
+
 const fixtures = require('./fixtures/transaction_builder')
 
 function constructSign (f, txb, useOldSignArgs) {

ts_src/transaction_builder.ts

@@ -146,6 +146,13 @@ export class TransactionBuilder {
     this.__TX = new Transaction();
     this.__TX.version = 2;
     this.__USE_LOW_R = false;
+    console.warn(
+      'Deprecation Warning: TransactionBuilder will be removed in the future. ' +
+        '(v6.x.x or later) Please use the Psbt class instead. Examples of usage ' +
+        'are available in the transactions-psbt.js integration test file on our ' +
+        'Github. A high level explanation is available in the psbt.ts and psbt.js ' +
+        'files as well.',
+    );
   }
 
   setLowR(setting?: boolean): boolean {