getting-started: replace usage of swh-storage/sql/bin/db-init by swh-db-init

see D538 in which this swh-db-init command is added.

docs/getting-started.rst

@@ -145,7 +145,7 @@ to your user, e.g.::
 
 You are done with object storage setup! Let's setup the database::
 
-  swh-storage/sql/bin/db-init softwareheritage-dev
+  swh-db-init storage -d softwareheritage-dev
 
 ``softwareheritage-dev`` is the name of the DB that will be created, it should
 match the ``db`` line in ``storage.yml``

[Phabricator Migration user]

Some references in the commit message have been migrated:

• D538 is now swh-core!16 (closed)