Add instructions for creating a new release

[nlhkabu]

This block is currently commented out on warehouse/templates/manage/project.html.

We should enable it and add help text.

[nlhkabu]

A sub ticket of #424

[nlhkabu]

To be clear, this is the message shown if there are no releases in a project. As @di raised in the meeting, it is not possible to create a project without a release.

However it is possible to delete all releases - so we should show a message in this instance.

Maybe something like:

No releases found.  <link to docs>Learn how to make a new release</link>

wdyt @di, @ewdurbin ?

[di]

I think this makes sense. Also worth mentioning that there are probably a lot of projects registered without releases via the legacy API, so this is worth doing.

[brainwane]

We talked about this a little in today's bug triage meeting. We may want to discuss what chunk of documentation we want to put here versus in the canonical packaging guide.