Merging with upstream

Duet code is contained in duet kernel.

To merge the master branch with the Linus' repository, go through the following steps:

1. Check whether a remote point to the upstream repository exists:

   $ git remote -v

   If it does, move to Step 3.

2. Configure a remote point to the upstream repository:

   $ git remote add upstream https://github.com/torvalds/linux.git

3. Sync the master branch:

   $ git fetch upstream

   $ git checkout master

   $ git merge upstream/master