Document `--network` flag in parent command

[Tofandel]

Some transients are registered with the method set_site_transient and have the form _site_transient_.. instead of _transient_ in the options table

Unfortunately the wp transient command has no way to accommodate those

[swissspidy]

That's what the --network flag is for. If you pass that, the commands use the *_site_transient functions.

Have you tried that?

[Tofandel]

Okay then that's a help command issue, the network flag does not appear in the list of flags available in wp help transient

It's only mentionned in

On a multisite installation, values are stored in the
  `wp_options` or the `wp_sitemeta` table, depending on use of the `--network`
  flag.

But that paragraph is a bit confusing for non multisite installs, which don't have this table

[swissspidy]

Good point, we should probably add some examples to the parent command.

You'll get --network examples for individual subcommands already though, e.g. with wp help transient delete