way 1 (from source):
go get github.com/eris-ltd/eris-cli
cd $GOPATH/src/github.com/eris-ltd/eris-cli
git fetch origin develop
git checkout develop
go install ./cmd/eris
eris init
way 2 (binary):
curl https://eris-iot-repo.s3.amazonaws.com/eris-deb/APT-GPG-KEY | sudo apt-key add -
echo "deb https://eris-iot-repo.s3.amazonaws.com/eris-deb {DIST} experimental" | sudo tee /etc/apt/sources.list.d/eris.list
apt-get update
apt-get install eris
eris init
replace {DIST} with the debian destribution (e.g. "jessie")