add link to admin interface

[eriktks]

Add a link to the admin interface in a prominent position on both the Software index page and the Projects index page, for example in the top menu: Software Projects Metrics Update About. This will lower the threshold for escience engineers to update the information on their software and projects. For the same reason, add a link from the admin interface to user instructions, for example to https://github.com/research-software-directory/research-software-directory/blob/master/docs/entering-data.md

[jspaaks]

Generally, I agree, except for the "prominent" part: our own employees are not the target audience for the web site.