Not everyone that uses this is a programming guru ... that should be kept in mind if you want to reach a wide audience of users.
Sure, but if you need to install a webmail, it's often that you have your own mail server and then, I hope you know what you do !! If running a mail server is not difficult, running a pretty secure one is more... And a misconfigured one could lead to many problems (such as Abuse report against yourself because you didn't block spammers to send through your host....)
So, YES, all users aren't programming guru, but installing a webmail SHOULD NOT be done unless you have some Server/Web Admin notions, and then, docs are pretty good (And I'm sure that it will be better ones when a stable release comes out.
JUST REMEMBER YOU'RE USING A SOFTWARE UNDER HUGE DEVELOPMENT, SO DON'T EXPECT TO GET AS MUCH AS A STABLE ONE !!!
Alex