docs(emailcomposer): add disclaimer to inform users that plugin doesn't work

src/plugins/emailcomposer.ts

@@ -8,6 +8,8 @@ declare var cordova;
  *
  * Requires Cordova plugin: cordova-plugin-email-composer. For more info, please see the [Email Composer plugin docs](https://github.com/katzer/cordova-plugin-email-composer).
  *
+ * DISCLAIMER: This plugin is experiencing issues with the latest versions of Cordova. Use at your own risk. Functionality is not guaranteed. Please stay tuned for a more stable version.
+ *
  * @usage
  * ```ts
  * import {EmailComposer} from 'ionic-native';