To add a Readme information window to your Kanban board, first, enable the Power-Up in Settings.
Describe how the team should use this particular board - what are the do’s and don’ts, whom to contact for the final say, etc. Feel free to add anything else that you think will be helpful for the team’s understanding of the workflow.
There are a few options for when the window is to open for users viewing. Given that you can make it show every time that the board gets opened - you could even use it as a company news page for the team!
If you’d rather keep a separate information box for each column, you can do that too - read more here.