dashboard/env/windows: instructions for setting up a buildlet

Updates golang/go#8640

Change-Id: I3f0b10c237f437137ed46415d7cc443d4c6a419b
Reviewed-on: https://go-review.googlesource.com/2269
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Andrew Gerrand <adg@golang.org>

dashboard/env/windows/README

@@ -0,0 +1,70 @@
+Unlike the other operating systems which have a bash script that runs
+on Linux and scripts qemu to prepare a GCE image, the Windows image
+builder image is prepared by hand, following this list of
+instructions:
+
+-- in GCE, create a new Windows 2008 server instance. Set its initial username
+   to "wingopher" and the password to something.
+
+-- boot it. first boot is slow.
+
+-- Connect with RDP to it. (I used the OS X Microsoft Remote Desktop
+   in the Mac App Store)
+
+-- In initial “Initial Configuration Tasks” window:
+   * disable automatic installation of updates. They’ll just interrupt
+     the builds later. And we don't care about security since this isn't
+     going to be Internet-facing. No ports will be accessible
+   * disable Windows Error Report (“Not participating”)
+
+TODO: disable the Windows firewall too. might break some outgoing net
+      tests? Figure out where to do this.
+
+-- Enable auto-login:
+   * Start > Run > Open: "control userpasswords2" [OK]
+   * Uncheck the "Users must enter a user name..." box (it already was
+     unchecked for me)
+   * Press "OK"
+   * Enter password twice.
+
+-- Download winstrap.
+   * Bring up cmd.exe (Start > Run > "cmd" [OK])
+   * Copy/paste (Right click: paste) this into cmd.exe:
+
+     bitsadmin /transfer mydownloadjob  /download /priority normal https://storage.googleapis.com/winstrap/winstrap-2015-01-03-440bb77.exe c:\users\wingopher\Desktop\winstrap.exe
+
+   * It should appear on the desktop.
+
+-- double click winstrap. type "go" and press <enter>. abort it once
+   it's downloaded everything. (close the window)
+
+-- make the Buildlet start on boot:
+   * Start > All Programs > right click "Startup"
+   * Right-mouse-drag "Start Buildlet" from the desktop (from winstrap) to the
+     Startup folder and "Create shortcuts here"
+
+-- Install git with middle option: "Use Git from Windows Command Prompt",
+   otherwise all the defaults.
+
+-- click yes yes yes on the tdm64-gcc installer question defaults.
+   Then do the tdm64-gcc installer again but do 32-bit this time. You
+   should then have two TDM installs at c:\TDM-GCC-64 and
+   c:\TDM-GCC-32.  Don’t pick other locations. The gobuilder adds
+   those to your path.
+
+TODO(bradfitz): this document is incomplete. Cover gcesysprep,
+regedit(?), windows-startup-script-cmd, etc.  And I think winstrap
+will need to write things to something outside of C:\Users, since
+sysprep on reboot nukes all users, at least on GCE. We probably need
+to run the buildlet's stage0 from the windows-startup-script-cmd. Find
+& ask Windows experts.
+
+-- 
+
+Docs:
+http://www.win2008workstation.com/configure-auto-logon/
+https://cloud.google.com/compute/docs/operating-systems/windows
+  -- notably "windows-startup-script-cmd" ala:
+     gcloud compute instances add-metadata <INSTANCE> --zone <ZONE> --metadata windows-startup-script-cmd="net user <USERNAME> <PASSWORD>"
+https://github.com/golang/winstrap
+http://golang.org/s/windowsbuilderhowto