Update README.markdown

Added missing step to change the value of Gallery.ConfirmEmailAddresses to false in Readme.

Change the value of Gallery.ConfirmEmailAddresses to false in Web.Config file under src\NuGetGallery, this is required to upload the packages after registration.
Merge pull request #1851 from bmanikm/patch-2

Update README.markdown to reflect a missing step that prevented packages from getting published.