update readme.md

Author: gregsaab

README.md

@@ -171,7 +171,29 @@ general_channel = channels.detect { |c| c.name == 'general' }
 
 ##### Upload a File
 
-Upload a file with [files_upload](https://api.slack.com/methods/files.upload).
+###### New Method
+
+Upload files with [sequenced API calls](https://api.slack.com/messaging/files#uploading_files).
+
+This library provides a helper method `files_upload_v2` that wraps the three separate API calls.
+
+```ruby
+contents = File.read('/users/me/results.pdf')
+client.files_upload_v2(
+  # required options
+  channels: 'C000000,C000001', # comma delimited channel ids, only one channel is required
+  filename: 'results.pdf', # this is used for the file title, unless a :title option is provided
+  contents: contents, # the string contents of the file
+  
+  # optional options
+  initial_comment: 'Sharing the Q1 results :tada:', # the message that is included with the file share thread
+  snippet_type: 'text', # the type of snippet
+  title: 'Q1 Results', # sets the title of the file, overriding the filename
+  thread_ts: '1738331487.481469' # specifies a thread to add this file to
+)
+```
+
+###### Legacy Method
 
 ```ruby
 client.files_upload(
@@ -184,6 +206,8 @@ client.files_upload(
 )
 ```
 
+The client.files_upload uses a deprecated endpoint `files.upload` that will [no longer be supported on 3/11/2025](https://api.slack.com/methods/files.upload#markdown).
+
 ##### Get Channel Info
 
 You can use a channel ID or name (prefixed with `#`) in all functions that take a `:channel` argument. Lookup by name is not supported by the Slack API and the `channels_id` method called invokes `conversations_list` in order to locate the channel ID. This invocation can have a cost if you have many Slack channels. In this scenario, we encourage you to use channel id.