Feat: tsrc add to add a new repository to the manifest

[cgestes]

Is your feature request related to a problem? Please describe.
It is hard to add a new repository to a manifest.

Describe the solution you'd like

$ tsrc add <local-path>
would you like to add <local-path> to your manifest:
path: <local-path>
url: <git-url>
branch: <branch>

Yeah something along those lines :)

[dmerejkowsky]

It is hard to add a new repository to a manifest.

What's hard? It's just a few lines of yaml. Or maybe I'm missing something ?

[cgestes]

the whole process is complex...
where is the manifest?
how do I test?
when should I push?
what do I do on mistakes? on syntax error...
etc...