add section to readme about eslint-plugin-chai-friendly

Author: chrisbreiding

README.md

@@ -12,10 +12,10 @@ npm install eslint-plugin-cypress --save-dev
 
 ## Usage
 
-Add an `.eslintrc` file to your `cypress` directory with the following:
+Add an `.eslintrc.json` file to your `cypress` directory with the following:
 
 ```json
-// my-project/cypress/.eslintrc
+// my-project/cypress/.eslintrc.json
 
 {
   "plugins": [
@@ -26,3 +26,26 @@ Add an `.eslintrc` file to your `cypress` directory with the following:
   }
 }
 ```
+
+## Chai and `no-unused-expressions`
+
+Using an assertion such as `expect(value).to.be.true` can fail the ESLint rule `no-unused-expressions` even though it's not an error in this case. To fix this, you can install and use [eslint-plugin-chai-friendly](https://www.npmjs.com/package/eslint-plugin-chai-friendly).
+
+```sh
+npm install --save-dev eslint-plugin-chai-friendly
+```
+
+In your `.eslintrc.json`:
+
+```json
+{
+  "plugins": [
+    "cypress",
+    "chai-friendly"
+  ],
+  "rules": {
+    "no-unused-expressions": 0,
+    "chai-friendly/no-unused-expressions": 2
+  }
+}
+```