[tex-live] Docu update proposal

[Richard J. Mathar]

Under section 3.2.3 "Directories" in http://tug.org/texlive/doc/texlive-en/texlive-en.html#installation

it's said

"This can be overridden by setting TEXDIR in the installer. The main reason to change it is if you lack write permission for the default location. "

This should better be

"This can be overridden by setting the shell environment variable
TEXLIVE_INSTALL_PREFIX before starting the installer.
The main reason to change it is if you lack write permission for the default
location, or if there is less than roughly 3.9 GB of space
left on the root partition on your file system."

Richard Mathar, mathar at mpia.de