Update schleuder.md with more detailed email command instructions.

See merge request !22

Those can still be useful as a disaster recovery mechanism.

This reverts commit deb01b72.

This is to please the linter, but it is also to make it look correctly
indented in the rendered version.

This script was used only in the previous webhook implementation but it
was superseded and is not deployed anymore so these instructions cannot
work currently.

This mainly adds the important bits for working with the new review apps
and staging environments in GitLab CI.

Details at tpo/web/team#15

A fellow Debian developer recommended this on Debian Planet, I haven't
test it myself.

... that's as much i could do in a reasonable amount of time, but
there's a lot of references to it everywhere. There's certainly still
stuff referencing git.tpo as well.