1) get binaries:
wget https://github.com/echochain/echo-core/files/2235017/gecho.v1.0-alpha.linux_x64.tar.gz
2) get source code
git clone https://github.com/echochain/echo-core.git
make all
From https://github.com/echochain/metamask/releases/tag/4.8.0 download the plugin