Running a WP-CLI command on multiple sites

[danielbachhuber]

We should have a document specifically focused on the different ways a WP-CLI can be run against multiple sites:

• [x] WP-CLI aliases
• [ ] Use wp find to produce a list of paths.

From https://github.com/wp-cli/ideas/issues/39

Related https://danielbachhuber.com/tip/run-wp-cli-command-wordpress-multisite/

[schlessera]

Aliases explained via #89