build instructions

[Ethan Bolker]

The current build instructions at
http://code.google.com/p/tree-buildingsurvey/wiki/BuildInstructions
(which are excellently detailed) call for a build from a zip file of
sources.

The build should start with checkout from svn. If the zip file is a
deliverable (e.g. for someone who wants to work elsewhere and not use
the project svn) then the build instructions should say how to create
it. If the zip file is only an artifact for the team-switch part of
the sprint then you shouldn't need it at all.