[Mailman] New list indoor@

[Roland Olbricht]

Hi all,

a couple of people, as announced
[here](https://community.openstreetmap.org/t/indoor-mapping-online-meeting/4442/20)
had a meeting on last Thursday, and we decided that we would like to
perpetuate that through a mailing list.

Could you please create a new mailing list indoor at openstreetmap.org? I'm
volunteering to administer the list.

Cheers,

Roland