You just add the following line to your local ~/.gemrc
file (it is in your home folder):
gem: --no-document
by
echo 'gem: --no-document' >> ~/.gemrc
or you can add this line to the global gemrc
config file.
Here is how to find it (in Linux):
strace gem source 2>&1 | grep gemrc
The --no-document
option is documented in the RubyGems CLI Reference.