Add emtpy rustfmt.toml to project root

If you have a rustmt.toml along your path, it will try to use
that configuration when running rustfmt. This is fixed by adding
a rustfmt.toml which is currently empty but which could be used
later on for setting up formatting rules.

Change-Id: I04e334866819d3648ab178f2ad3ad44872166fdc
Signed-off-by: Adam Snaider <adsnaider@gmail.com>
diff --git a/rustfmt.toml b/rustfmt.toml
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/rustfmt.toml