Add OSX wheel generation instructions and upload script

RELEASE.txt

@@ -34,6 +34,10 @@ How to make a new release of ``skimage``
    python setup.py register
    python setup.py sdist upload
 
+  Go to https://travis-ci.org/scikit-image/scikit-image-wheels,
+  select the "Current" tab, and click (on the right) on the "Restart Build"
+  icon.  After that finished, execute ``tools/osx_wheel_upload.sh``.
+
 - Increase the version number
 
   - In ``setup.py``, set to ``0.Xdev``.

tools/osx_wheel_upload.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+# Script to download / check and upload scikit_image wheels for release
+RACKSPACE_URL=http://a365fff413fe338398b6-1c8a9b3114517dc5fe17b7c3f8c63a43.r19.cf2.rackcdn.com
+if [ "`which twine`" == "" ]; then
+    echo "twine not on path; need to pip install twine?"
+    exit 1
+fi
+cd scikit-image
+SK_VERSION=`git describe --tags`
+if [ "${SK_VERSION:0:1}" != 'v' ]; then
+    echo "scikit image version $SK_VERSION does not start with 'v'"
+    exit 1
+fi
+WHEEL_HEAD="scikit_image-${SK_VERSION:1}"
+WHEEL_TAIL="macosx_10_6_intel.macosx_10_9_intel.macosx_10_9_x86_64.whl"
+mkdir -p wheels
+cd wheels
+rm -rf *.whl
+for py_tag in cp27-none cp33-cp33m cp34-cp34m
+do
+    wheel_name="$WHEEL_HEAD-$py_tag-$WHEEL_TAIL"
+    wheel_url="${RACKSPACE_URL}/${wheel_name}"
+    curl -O $wheel_url
+    if [ "$?" != "0" ]; then
+        echo "Failed downloading $wheel_url; check travis build?"
+        exit $?
+    fi
+done
+cd ..
+twine upload wheels/*.whl