docs: add reuse device option (#75)

Author: Vasil Chimev

README.md

@@ -152,6 +152,7 @@ As you can see, the `app` property can be left an empty string which will force
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 |runType| Select the capabilities from your config file `appium.capabilities.json`| Consider using `android`, `device`, `sim` strings as part of your `runType` option if you haven't provided `app` capability. Thus, the runner will look for app package in the right location for the current run. <br/> e.g. --runType ios-device10iPhone6|
 |appPath| Provide location of the app package to be tested. This will overwrite all provided capabilities for app| Possible values are:<br/> - app build package name (in case `--sauceLab` option is set it will prepend `sauce-storage:` in front of the app name so app has to be [uploaded to Sauce Labs](https://wiki.saucelabs.com/display/DOCS/Uploading+Mobile+Applications+to+Sauce+Storage+for+Testing) before execution starts)<br/> - path e.g. `platforms/android/build/outputs/apk/demo.apk`.<br/> Example: --appPath demo-debug.apk|
+| reuseDevice | Reuse the device specified in the `runType` capabilities. If the emulator/simulator is not running, it will launch, execute tests and remain running. The next execution of `npm run e2e` with the `reuseDevice` option will attach to the already running emulator/simulator, execute tests and keep it running. | e.g. --reuseDevice |
 |sauceLab| Enable tests execution in [Sauce Labs](https://saucelabs.com/). As a prerequisite you will have to define `SAUCE_USER` and `SAUCE_KEY` as [environment variable](https://wiki.saucelabs.com/display/DOCS/Best+Practice%3A+Use+Environment+Variables+for+Authentication+Credentials)| e.g. --sauceLab|
 |capsLocation| Change the location where `appium.capabilities.json` config file can be. It should be relative to the root directory | e.g. --capsLocation /e2e-tests|
 |port| Appium server port|