Add an upgrade guide (#370)

UPGRADING.md

@@ -0,0 +1,57 @@
+# Upgrade Guide
+
+## 5.x to 6.x
+
+_Our Ruby library has gone through some major improvements and there are a few
+changes required to use the new integrations_
+
+#### Capistrano and deploys
+
+Support for notifying Bugsnag of deployments has been separated into a separate
+gem named `bugsnag-capistrano`. See the [integration
+guide](https://docs.bugsnag.com/platforms/ruby/capistrano) for more information.
+
+
+#### Configuration
+
+* `Configuration.use_ssl` has been removed. Include the preferred protocol in `Configuration.endpoint` instead.
+  ```diff
+    Bugsnag.configure do |config|
+  -   config.use_ssl = true
+  -   config.endpoint = 'myserver.example.com'
+  +   config.endpoint = 'https://myserver.example.com'
+    end
+  ```
+* `Configuration.ignore_classes` now no longer accepts strings. Use classes directly instead.
+* `Configuration.delay_with_resque` has been removed
+* `Configuration.vendor_paths` has been removed
+* `Configuration.params_filters` has been renamed to `Configuration.meta_data_filters` to be clearer
+
+#### Notifying
+
+* `notify` now only supports block syntax. Replace usage of the overrides hash with a block
+
+  ```diff
+  - Bugsnag.notify(e, {severity: 'info'})
+  + Bugsnag.notify(e) do |report|
+  +   report.severity = 'info'
+  + end
+  ```
+
+* `Bugsnag.notify_or_ignore` and `Bugsnag.auto_notify` have been removed removed. Call `notify` directly instead.
+* `after_notify_callbacks` has been removed
+* `Bugsnag::Notification` has been renamed to `Bugsnag::Report`
+
+#### Logging
+
+* `config.debug` boolean has been removed. Set the logger level directly
+
+  ```diff
+  + require 'logger'
+
+    Bugsnag.configure do |config|
+      # .. set API key and other properties
+  -   config.debug = true
+  +   config.logger.level = Logger::DEBUG
+    end
+  ```