Add README

README.markdown

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+# What is Vigilo?
+
+Vigilo is a dead-simple file system watcher for Ruby.
+
+# API
+
+    Vigilo::Watcher.watch(dir1, dir2) do |changed, added, deleted|
+      # created is an Array of files changed, or nil if none changed
+      # added is an Array of files added, or nil if none added
+      # deleted is an Array of files deleted, or nil if none deleted
+    end
+
+You can also start a watch inside a thread to keep it going in the
+background.
+
+# Resource usage
+
+On my Mac, the portable (polling) backend used 2.5% CPU while the
+FSEvents backend used 0.4% CPU.
+
+# In progress
+
+Vigilo is brand new and currently only has support for FSEvents and File
+System polling. Support for inotify is coming.
+
+At the moment, I have only tested it on my local machine and the final
+API isn't in place, so feel free to look, but don't rely on anything
+just yet.
+
+Tests are in progress.
+