You have been assigned a GitHub pull request to cherry-pick or merge the changes do the following:

git remote add reponame URL

Like so:

git remote add knowledgejunkie https://github.com/knowledgejunkie/mythtv.git

Then fetch the content:

git fetch reponame

If the contribution consists of a separate branch off master for just this pull request, then you can merge that remote branch with:

git merge reponame/branchname

In case you want to only pick some commits of the contribution you can check the commit you want to get at the GitHub pull request page and simply do:

git cherry-pick -s sha1_commit

For more information on cherry-pick options see UsingGit#Usefulgitcommands Notice that the latter will not automatically close the pull request.