add a readme

it should

- tell you how to build
- tell you how to set up a server
- tell you how to connect to a server
- tell you the basic controls (ex: delete for clear)
- say the window needs to be of a specific size or it won't properly and the chat won't render (Limitations section)

Start by inspecting the repository's existing build information and the server and client entry points. Add a README covering building, server setup and connection, basic controls such as Delete for clearing, and a Limitations section describing the required window size and chat rendering issue.

Written by the indexing model from the issue text.