Github 上怎样把新 commits 使用在自己的 fork 上？

Step 3: Configure remotes

When a repo is cloned, it has a default remote called origin that points to your fork on GitHub, not the original repo it was forked from. To keep track of the original repo, you need to add another remote named upstream:

$ cd Spoon-Knife
# Changes the active directory in the prompt to the newly cloned "Spoon-Knife" directory
$ git remote add upstream https://github.com/octocat/Spoon-Knife.git
# Assigns the original repo to a remote called "upstream"
$ git fetch upstream
# Pulls in changes not present in your local repository, without modifying your files

Pull in upstream changes

If the original repo you forked your project from gets updated, you can add those updates to your fork by running the following code:

$ git fetch upstream
# Fetches any new changes from the original repo
$ git merge upstream/master
# Merges any changes fetched into your working files