Update readme with the new input (#323)

Author: tothszabi

README.md

@@ -131,6 +131,7 @@ Build a development IPA with custom xcconfig file path:
 | `log_formatter` | Defines how `xcodebuild` command's log is formatted.  Available options:  - `xcpretty`: The xcodebuild command's output will be prettified by xcpretty. - `xcodebuild`: Only the last 20 lines of raw xcodebuild output will be visible in the build log.  The raw xcodebuild log will be exported in both cases. | required | `xcpretty` |
 | `automatic_code_signing` | This input determines which Bitrise Apple service connection should be used for automatic code signing.  Available values: - `off`: Do not do any auto code signing. - `api-key`: [Bitrise Apple Service connection with API Key](https://devcenter.bitrise.io/getting-started/connecting-to-services/setting-up-connection-to-an-apple-service-with-api-key/). - `apple-id`: [Bitrise Apple Service connection with Apple ID](https://devcenter.bitrise.io/getting-started/connecting-to-services/connecting-to-an-apple-service-with-apple-id/). | required | `off` |
 | `register_test_devices` | If this input is set, the Step will register the known test devices on Bitrise from team members with the Apple Developer Portal.  Note that setting this to yes may cause devices to be registered against your limited quantity of test devices in the Apple Developer Portal, which can only be removed once annually during your renewal window. | required | `no` |
+| `test_device_list_path` | If this input is set, the Step will register the listed devices from this file with the Apple Developer Portal.  The format of the file is a comma separated list of the identifiers. For example: `00000000–0000000000000001,00000000–0000000000000002,00000000–0000000000000003`  And in the above example the registered devices appear with the name of `Device 1`, `Device 2` and `Device 3` in the Apple Developer Portal.  Note that setting this will have a higher priority than the Bitrise provided devices list. |  |  |
 | `min_profile_validity` | If this input is set to >0, the managed Provisioning Profile will be renewed if it expires within the configured number of days.  Otherwise the Step renews the managed Provisioning Profile if it is expired. | required | `0` |
 | `certificate_url_list` | URL of the code signing certificate to download.  Multiple URLs can be specified, separated by a pipe (`\|`) character.  Local file path can be specified, using the `file://` URL scheme. | required, sensitive | `$BITRISE_CERTIFICATE_URL` |
 | `passphrase_list` | Passphrases for the provided code signing certificates.  Specify as many passphrases as many Code signing certificate URL provided, separated by a pipe (`\|`) character.  Certificates without a passphrase: for using a single certificate, leave this step input empty. For multiple certificates, use the separator as if there was a passphrase (examples: `pass\|`, `\|pass\|`, `\|`) | sensitive | `$BITRISE_CERTIFICATE_PASSPHRASE` |