How do I import an external library from github in robotframework?

I want to import https://github.com/Legrandgroup/robotframework-modbuslibrary library in my project. I have a test suite modbus_test.robot where I want to use the modbuslibrary. There would be no problem if I just pip installed. I have to do without using pip and yet getting access to all the keywords there. How can I achieve this?