cli: Prevent rewrapping of code blocks

Before:

```
$ swh db init -h
Usage: swh db init [OPTIONS] MODULE

  Initialize a database for the Software Heritage <module>.

  The database connection string comes from the configuration file (see option
  ``--config-file`` in ``swh db --help``) in the section named after the
  MODULE argument.

  Example::

      $ cat conf.yml     storage:       cls: postgresql       db:
      postgresql://user:passwd@pghost:5433/swh-storage       objstorage:
      cls: memory

      $ swh db -C conf.yml init storage  # or     $
      SWH_CONFIG_FILENAME=conf.yml swh db init storage

  Note that the connection string can also be passed directly using the '--db-
  name' option, but this usage is about to be deprecated.
```

After:

```
$ swh db init -h
Usage: swh db init [OPTIONS] MODULE

  Initialize a database for the Software Heritage <module>.

  The database connection string comes from the configuration file (see option
  ``--config-file`` in ``swh db --help``) in the section named after the
  MODULE argument.

  Example::

          $ cat conf.yml
          storage:
            cls: postgresql
            db: postgresql://user:passwd@pghost:5433/swh-storage
            objstorage:
              cls: memory

          $ swh db -C conf.yml init storage  # or
          $ SWH_CONFIG_FILENAME=conf.yml swh db init storage

  Note that the connection string can also be passed directly using the '--db-
  name' option, but this usage is about to be deprecated.
```