LTSP Upstream Documentation
You can find the latest upstream documentation as a PDF here: https://sourceforge.net/projects/ltsp/files/Docs-Admin-Guide/LTSPManual.pdf/download
As well, you can find an lts.conf.5 manpage you can drop into /usr/local/man/man5, or wherever your distro allows you to install user manpages here: https://sourceforge.net/projects/ltsp/files/Docs-Admin-Guide/lts.conf.5/download
As well, some distros are now including the LTSP docs as a package. Search for the "ltsp-docs" package in your package management system.
The source for the LTSP documentation is maintained in docbook, and can be downloaded as a BZR branch from Launchpad.net. You can find the LTSP docs in the ltsp-docwriters user.
Becoming an LTSP documenter
If you'd like to help with LTSP documentation, and know a bit of docbook, please contact Scott at sbalneav at ltsp.org