Custom Group Chart (simple newbie urgent help!)

Hi, I am v new to Power BI, most grateful for help with the following query.

I would like a view of data which looks like the attached image, which is basically a custom grouping of Companies with number of customers with low customers (640 or below) medium no of customers (640 to 740 suppliers) and high number of suppliers, (740 or above)

My Data Set is a simple .csv / excel file as below. 

It seems a simple query, but I just can't work out how to do it optimally... any advice gratefully received. I can do it in Excel but need to create custom calculations which is sub-optimal