如何从一个远程分支拉到另一个分支？

For safety reason, my supervisor doesn't allow me to pull his work directly from the master branch. So I created one branch remotely named 'subbranch' and clone it to my local repository. How could I let 'subbranch' keep up to date with the master branch? I just know how to use the GUI to do it. How to do it with command line?For safety reason, my supervisor doesn't allow