TARGET  Landing onto "master", the default target under git.
 REMOTE  Using remote "origin", the default remote under git.
 Select a Default Commit Range 

You're running a command which operates on a range of revisions (usually,
from some revision to HEAD) but have not specified the revision that should
determine the start of the range.

Previously, arc assumed you meant 'HEAD^' when you did not specify a start
revision, but this behavior does not make much sense in most workflows
outside of Facebook's historic git-svn workflow.

arc no longer assumes 'HEAD^'. You must specify a relative commit explicitly
when you invoke a command (e.g., `arc diff HEAD^`, not just `arc diff`) or
select a default for this working copy.

In most cases, the best default is 'origin/master'. You can also select
'HEAD^' to preserve the old behavior, or some other remote or branch. But you
almost certainly want to select 'origin/master'.

(Technically: the merge-base of the selected revision and HEAD is used to
determine the start of the commit range.)

    What default do you want to use? [origin/master]