How do I type a table in markdown?

Our forum software can render tables like this one:

Good Avg Poor
Yes 50 30 10
No 30 30 20

It’s pretty easy to type this sort of thing in using Markdown - just type one line per row separate the data entries with pipes (|). You also need a special row to to indicate the headers. The exact markdown for the table above is:

|   |Good|Avg|Poor|