adds guides/.document to tell rdoc not to process this directory

When the Rails 4 gem is installed rdoc sees markdown files below the
guides directory and processes them. With an empty .document file
we prevent that from happening. Thanks to @drbrain for the tip.

1 files changed, 0 insertions, 0 deletions

diff --git a/guides/.document b/guides/.document
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/guides/.document