How do I join all the channels in my weechat layout?

Okay, after asking around in the freenode #weechat channel a bit I finally got this:

• Download the autojoin.py script to ~/.weechat/python/autoload
• Run /python autoload to load the script
• Run /autojoin --run to store the channels to join
• Run /layout store to store the order of the channels
• Run /save to save your settings to a file

Next time you start weechat and connect to a server the channels you were connected to when you did these steps will be joined for you.