Its useful to sync a fork when contributing to open source project.

Here is some tips:

1. make sure current folder is repo root.
2. add upstream link. Here, upstream could be any name git remote add upstream https://github.com/whoever/whatever.git
3. fetch content. ```git fetch upstream`
4. goto your branch and merge (keep local changes) or rebase (do not keep) upstream branch.

Reference:

1. https://stackoverflow.com/questions/7244321/how-do-i-update-a-github-forked-repository
2. https://help.github.com/en/articles/syncing-a-fork