Update README.md to refer to homebrew Formula

Summary: Release builds should probably favor using
@marpaia's brew Formula to get a release build.

Leave the boostrap script around to simplify building
from master.

Closes #229

Reviewed By: @jwatzman

Differential Revision: D2184416

README.md

@@ -69,10 +69,9 @@ In the folly directory, run
 
 OS X (Homebrew)
 ----
-There is a bootstrap script if you use Homebrew (http://brew.sh/). At the time
-of writing (OS X Yosemite 10.10.1) the default compiler (clang) has some
-issues building, but gcc 4.9.2 from Homebrew works fine. (This is taken care
-of by the bootstrap script.)
+folly is available as a Formula and releases may be built via `brew install folly`.
+
+You may also use `folly/bootstrap-osx-homebrew.sh` to build against `master`:
 
 ```
   cd folly