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

Using the GitHub pull request page, check the commit you want to get and simply do:

git cherry-pick -s sha1_commit

An alternative way is using the GitHub instructions: ​https://help.github.com/articles/merging-a-pull-request#merging-locally