Configuration files for mr.

IMPORTANT:

In this mr repository do not add any file that may conflict with files from
any other repository managed by vcsh.

Examples of conflicting files are ~/README, ~/LICENSE, or ~/.gitmodules

This is required because this repository is meant to be cloned before all the
other ones in order to bring them in.

In particular this means that the vcsh configuration required to handle sparse
checkouts and colliding files may still not be in place when this repository
is cloned.