Well, you have to change additional information
to your wished content:
\extrainfo{\faGithub\href{https://github.com/}{ name}}% <===============
Please see with the current version of moderncv
(version 2.0.0) you can use command
\social[github]{jdoe}
to add your github informations.
Please see the following MWE
\documentclass[11pt,a4paper,sans]{moderncv}
% moderncv themes
\moderncvstyle{classic} % casual, classic, banking, oldstyle and fancy
\moderncvcolor{blue}
\usepackage[utf8]{inputenc}
\usepackage[scale=0.75]{geometry}
\usepackage{booktabs}
\usepackage{fontawesome}% <=============================================
% personal data
\name{John}{Doe}
\title{Resumé title}
\address{street and number}{postcode city}{country}
\phone[mobile]{+1~(234)~567~890}
\phone[fixed]{+2~(345)~678~901}
\phone[fax]{+3~(456)~789~012}
\email{[email protected]}
\homepage{www.johndoe.com}
\social[linkedin]{john.doe}
\social[twitter]{jdoe}
\social[github]{jdoe} % <===============================================
\extrainfo{\faGithub\href{https://github.com/}{ name}}% <===============
\photo[64pt][0.4pt]{example-image-a}
\quote{Some quote}
\setlength{\footskip}{66pt}
\begin{document}
\makecvtitle
\section{Education}
\cventry{year--year}{Degree}{Institution--3}{City--4}{\textit{Grade}--5}{Description--6} % arguments 3 to 6 can be left empty
\cventry{year--year}{Degree}{Institution}{City}{\textit{Grade}}{Description}
\section{Master thesis}
\cvitem{title}{\emph{Title}}
\cvitem{supervisors}{Supervisors}
\cvitem{description}{Short thesis abstract}
\end{document}
with the result:
