UPGRADING.md in slack-ruby-client-1.1.0 vs UPGRADING.md in slack-ruby-client-2.0.0

@@ -1,7 +1,35 @@
 Upgrading Slack-Ruby-Client
 ===========================
 
+### Upgrading to >= 2.0.0
+
+[#416](https://github.com/slack-ruby/slack-ruby-client/pull/416) Removes default values for Faraday's SSL settings `ca_file` and `ca_path`.
+
+If you previously relied on `OpenSSL::X509::DEFAULT_CERT_FILE` or `OpenSSL::X509::DEFAULT_CERT_DIR` to set these values you must now do so explicitly. E.g.:
+
+```ruby
+Slack::Web::Client.configure do |config|
+  config.ca_file = OpenSSL::X509::DEFAULT_CERT_FILE
+  config.ca_path = OpenSSL::X509::DEFAULT_CERT_DIR
+end
+```
+
+or
+
+```ruby
+client = Slack::Web::Client.new(ca_file: OpenSSL::X509::DEFAULT_CERT_FILE, ca_path: OpenSSL::X509::DEFAULT_CERT_DIR)
+```
+
+#### RealTime Stores
+
+Slack has deprecated the `rtm.start` method and [replaced its response](https://api.slack.com/changelog/2021-10-rtm-start-to-stop) with that of `rtm.connect`, so it has been removed from the library along with the `start_method` configuration ([#419](https://github.com/slack-ruby/slack-ruby-client/pull/419)) and `Slack::RealTime::Stores::Starter` is now the default store.
+If your app still relies on the old `rtm.start` behavior, you can achieve a similar result with `Slack::RealTime::Stores::Store`, which initializes itself using Web API methods (see [README](README.md#slackrealtimestoresstore)).
+
+The names of the Store caches `channels` and `groups` have been changed to `public_channels` and `private_channels` to reflect their true meaning.
+This is consistent with the [Slack Web API](https://api.slack.com/methods/conversations.list#arg_types), although [event types for private channels](https://api.slack.com/events?query=group) still use the term `group`.
+In both cases, private channels consist of both [conversation types](https://api.slack.com/types/conversation) (`id: 'C...'', is_channel: true, is_group: false, is_private: true`) and [group types](https://api.slack.com/types/group) (`id: 'G...', is_channel: false, is_group: true, is_private: true`) depending whether the object was created before or after March 2021.
+
 ### Upgrading to >= 1.0.0
 
 #### Deprecated Methods
 
 Slack has deprecated all `channel` and `group` methods, which have been removed from the library.