Information about commands and mapping functions to them

[nburns]

I think it could be very helpful if learnvimscriptthehardway had a bit about how to map functions to commands somewhere around the "Functions" section or "Function Arguments" section.

Specifically if there was an example where someone was walked through the process of defining a function in their vimrc and then mapped it to a command.

learnvimscriptthehardway is my favorite resource for finding out how to do things in vim, and I had to do some googling and reading :help command to figure out how to do this