Document adding OSX keychain to Jenkins configuration

[cowwoc]

The script outputs:

The OS X Keychain password for builds is ABC
You will need to copy this into the Jenkins configuration on bbs
for every project that will be compiled on this slave, or copy a special
per-project Keychain to /Users/builds/Library/Keychains.

I have no idea what this means. It's not clear where I need to enter the keychain password in Jenkins. Please document the steps (which menus to go into) and possibly even include screenshots.