Updated readme

Author: mitsuhiko

README.md

@@ -1,4 +1,7 @@
 # sentry-cli
 
 This is a work in progress sentry command line client for some
-generic tasks.  This currently requires nightly rust to compile.
+generic tasks.  Right now this is primarily used to upload
+debug symbols to Sentry if you are not using the fastland
+tools.  This currently requires nightly rust to compile and
+because of this binaries for OS X are provided.