Update README with instructions

README.md

@@ -1,7 +1,38 @@
 # Custom Error Test Helper
 
-Library for testing Solidity custom errors with Truffle/Ganache.
+Library for testing Solidity custom errors with [Truffle](https://trufflesuite.com/truffle)/[Ganache](https://github.com/trufflesuite/ganache/releases).
 
-## Usage:
+## Installation
 
-WIP
+```bash
+npm install --save-dev custom-error-test-helper
+```
+
+## Usage
+
+Import `custom-error-test-helper` in your test files to access the assertion.
+
+```js
+const { expectRevertCustomError } = require("custom-error-test-helper");
+
+const MyContract = artifacts.require("MyContract");
+
+contract("MyContract", function (accounts) {
+  beforeEach(async function () {
+    this.contract = await MyContract.new();
+  });
+
+  it("reverts with an error with no parameters", async function () {
+    // error SomeError0();
+    await expectRevertCustomError(MyContract, this.contract.someFunction0(), "SomeError0");
+  });
+
+  it("reverts with an error with parameters", async function () {
+    // error SomeError1(uint256 one, address vb);
+    await expectRevertCustomError(MyContract, this.contract.someFunction1(), "SomeError1", [
+      1,
+      "0xAb5801a7D398351b8bE11C439e05C5B3259aeC9B",
+    ]);
+  });
+});
+```