Have `datalad-make` initialize the git annex remote

[mih]

The git-annex initremote step is listed as an explicit task for a user in the readme.

I believe that this should be done by datalad-make internally and as-needed. Reasons:

• the particular invocation never changes
• the system does not work without this initialization

A user can only forget it and face errors, or copy the line exactly. A machine should do this IMHO.