Include backtrace i/o as a crash reporter backend option

Note: I have no affiliation with this company - just thought this would be helpful for people

docs/api/crash-reporter.md

@@ -24,6 +24,10 @@ following projects:
 * [socorro](https://github.com/mozilla/socorro)
 * [mini-breakpad-server](https://github.com/electron/mini-breakpad-server)
 
+Or use a 3rd party hosted solution:
+
+* [Backtrace I/O](https://backtrace.io/electron/)
+
 Crash reports are saved locally in an application-specific temp directory folder.
 For a `productName` of `YourName`, crash reports will be stored in a folder
 named `YourName Crashes` inside the temp directory. You can customize this temp