It is possible to add documentation files to already installed packages issuing the following commands in any terminal (both commands may need root privileges depending on how you installed Tex Live in the first place and the second is UNIX only):
tlmgr option docfiles 1
sets the docfiles option to 1, i.e. from now on
tlmgr will download and install documentation files every time a new package is installed. If during the installation process of TeX Live the user chooses not to install docs, this option is automatically set to 0, so you need to manually change its value.
tlmgr install --reinstall $(tlmgr list --only-installed | sed -e 's/^i //' -e 's/:.*$//')
the above command reinstalls all packages listed by
tlmgr list --only-installed, i.e. all already installed packages. The
sed part is used to remove everything except the package name from the list generated by
tlmgr list --only-installed. As an example, before the
sed part the first line of the list looks like:
i 12many: Generalising mathematical index sets.
while after the
sed treatment it looks like:
For more info see the
sed docs. Credit goes to Norbert Preining, see this thread on comp.tex.live