adds info on how to generate html reports (#141)

Author: zecarrera

packages/lighthouse/README.md

@@ -194,7 +194,7 @@ The audits are things like the first meaningful paint and the score is provided
 
 When using custom tools, it can be convenient to directly access the raw information they provide for doing manual things, such as generating a custom reports.
 
-To do so, you can pass a `callback` function to the task initializer. Then, when an audit is run, this callback will we executed with the raw data of the underlying tool.
+To do so, you can pass a `callback` function to the task initializer. Then, when an audit is run, this callback will be executed with the raw data of the underlying tool.
 
 In the `cypress/plugins/index.js` file:
 
@@ -214,6 +214,56 @@ module.exports = (on, config) => {
 };
 ```
 
+#### Generating HTML reports
+
+In order to have lighthouse's HTML reports available in your filesystem, you'll need to first specify `html` as the ouput for your lighthouseConfig.
+
+```js
+const thresholds = {
+  /* ... */
+};
+
+const lighthouseOptions = {
+  /* ... your lighthouse options */
+};
+
+const lighthouseConfig = {
+  output: 'html' //If output is not specified, then the json report will be generated
+  /* ... your lighthouse configs */
+};
+
+cy.lighthouse(thresholds, lighthouseOptions, lighthouseConfig);
+```
+
+Secondly, whilst reading the raw report use `fs` to write the HTML report to disk.
+
+```javascript
+const { lighthouse, prepareAudit } = require("@cypress-audit/lighthouse");
+const fs = require('fs');
+
+module.exports = (on, config) => {
+  on("before:browser:launch", (browser = {}, launchOptions) => {
+    prepareAudit(launchOptions);
+  });
+
+  on("task", {
+    lighthouse: lighthouse((lighthouseReport) => {
+      console.log('---- Writing lighthouse report to disk ----');
+
+            fs.writeFile(
+                'lighthouse.html',
+                lighthouseReport.report,
+                (error: any) => {
+                    error
+                        ? console.log(error)
+                        : console.log('Report created successfully');
+                },
+            );
+    }),
+  });
+};
+```
+
 ## Good to know
 
 ### Test with a production bundle