readme: notes for config & trace-processor usage

Author: paulirish

readme.md

@@ -60,6 +60,43 @@ cd ../lighthouse-cli/
 npm link lighthouse-core
 ```
 
+## Custom run configuration
+
+You can supply your own run configuration to customize what audits you want details on. Copy the [default.json](https://github.com/GoogleChrome/lighthouse/blob/master/lighthouse-core/config/default.json) and start customizing. Then provide to the CLI with `lighthouse --config-path=$PWD/myconfig.json <url>`
+
+## Trace processing
+
+Lighthouse can be used to analyze trace and performance data collected from other tools (like WebPageTest and ChromeDriver). The `traceContents` and `performanceLog` artifact items can be provided using a string for the absolute path on disk. The perf log is captured from the Network domain (a la ChromeDriver's [`enableNetwork` option](https://sites.google.com/a/chromium.org/chromedriver/capabilities#TOC-perfLoggingPrefs-object) and reformatted slightly. As an example, here's a trace-only run that's also evaluating just user-timings:
+
+##### `config.json`
+```js
+{
+ "audits": [
+  "user-timings"
+ ],
+
+ "artifacts": {
+   "traceContents": "~/code/lighthouse-core/test/fixtures/traces/trace-user-timings.json",
+   "performanceLog": "~/code/lighthouse-core/test/fixtures/traces/perflog.json"
+ },
+
+ "aggregations": [{
+   "name": "Performance Metrics",
+   "description": "These encapsulate your app's performance.",
+   "scored": false,
+   "categorizable": false,
+   "items": [{
+     "criteria": {
+       "user-timings": { "rawValue": 0, "weight": 1 }
+     }
+   }]
+ }]
+}
+```
+
+Then, run with: `lighthouse --config-path=$PWD/config.json http://www.random.url`
+
+
 ## Tests
 
 Some basic unit tests forked are in `/test` and run via mocha. eslint is also checked for style violations.